Ok, so just saw that a few days posts lost due to tech hitch so I will rehash what I wrote (if I can remember) if some of it is of any use.
Firstly it is well worth flying into Cairns at that time of the year and will allow you to see some of the natural beauty of Far North Qld (FNQ) which is often missed in many itineraries for many reasons.
There is many things to see and do along your whole planned trip so I will just list a few things I think are worth doing while you are in FNQ and NQ.
I am no fan of Cairns the city however of course there is things to see and do. One of the the old favourite tourist attractions is the Kuranda Scenic Rail / Skyrail which winds its way through the rainforest of the Kuranda range, destination Kuranda which is a hippy type tourist town with markets etc selling all sorts of crystals and wind chimes

While I am not a fan of markets many love this place and it is very pretty. The best way to go is up by train on the old rail and down by Skyrail (gondalas). This gives spectacular views over Cairns and surrounds as it glides over the rainforest canopy. Beautifully constructed to avoid environmental damage as required by the approvals to build.
OK, so some other suggestions. Firstly a road trip south from Cairns wouldn't be complete without
first going North.
1. The road from Cairns to Mossman / Port Douglas is an unheralded lovely drive. When I lived in Cairns over 30 years ago sometimes I had to work in Mossman and one of the great pleasures was punting the Lav along this road early in the morning with the sun rising over the water. Of course won't be quite the same in a car however there are some lovely beach communities along the way. Mossman is a sugar farming town and Port Douglas is a very popular tourist town which isn't on my list of favourites but has it's own attractions. Many might remember when Bill Clinton stayed at the new Christopher Skase resort there many years ago and visited the reef from there (IIRC) Anyway, if you want a T Shirt or a Marlin Fishing trip Port Douglas is the place!!
2. I had mentioned that a trip to historic Cooktown would be doable and interesting because the inland road is now fully sealed, however the drawback is you can't do the loop and come back the coast road through the Daintree Rainforest because it is 4wd only.
3. Daintree Rainforest and Mossman Gorge. The Daintree is Australia's largest rainforest and well worth a visit. This can still easily be done by a day tour leaving from Port Douglas / Mossman or even Cairns.
4.
Atherton Tableland - Close to Cairns and accessed by road up the Kuranda range or via the Gillies Highway. The Gillies is a famous road well liked by the motorcycling fraternity because of its climb up over 800m via 263 bends in 19kms of road. (TBH was always quite a handful on the triple coming down - a smaller more nimble bikes would have been ideal!)
The Atherton Tablelands is a beautiful area to explore with many waterfalls, crater lakes, rainforest walks all within a relatively short distance. Many places to stay but towns such as Malanda, Yungaburra or Atherton are good. Much cooler up there but time of year should hopefully get lovely clear warn days (if it stays drizzly or low cloud of course will stay chilly)
5. I had previously mentioned going to places like Chillagoe and even Cobold Gorge which was only discovered some 30 odd years ago, has permanent water and can only be explored by tour boats. Some of these places would not be suitable to take a hire car however I also mentioned the
Savannahlander train which goes as far as Forsayth (fairly remote) and this apparently can be done over a number of days with side tours to
Chillagoe Caves, Cobold Gorge and Undara Lava Tubes - These are all spectacular places and well worth visiting (a lot of Australians haven't been to some of these) I think you can start this trip in Cairns, which would start with the Kuranda rail but no doubt there are places on the Tablelands you can also board.
6. Leaving the Atherton Tabeland my preference would be to head west but limited time mean best bang for buck would be head back to the coast via
Milla Milla and down the Palmerston Highway, another nice range road. A number of things to see along here including the
Mamu Tropical Skywalk erected on the side of the range, however one unusual one is to head to
Paronella Park. (Best I let you read for yourself as it is hard to describe -
https://www.paronellapark.com.au/ ) Very beautiful and unique place.
7. Heading South you could also go white water rafting on the
Tully River (at Tully) although time of the year may mean water levels not high enough or have some R&R at
Mission Beach or go hiking on Hinchinbrook Island
8. Heading further south you pass through other lovely areas such as Cardwell and Ingham, with their own attractions however next major city is
Townsville. Townsville was a major military base in WW2 and was actually attacked with no damage and still has a large defence presence. Townsville is not a renowned tourist town however has many interesting things to see.
The strand is a vibrant walking / cafe / bar / restaurant precinct with an enclosed sea water lagoon at the end. Beside that is
Kissing Point which has an interesting walk that includes a walk past preserved fortification areas including interactive displays, a boardwalk beside the water and some tracks through garden areas with natural vegetation.
9.
Magnetic Island is a short ferry ride from Townsville (basically a suburb) and a popular tourist destination.
10. Heading South from Townsville after passing through the Burdekin (Australias largest sugar growing area) including crossing the famous
Burdekin bridge, the next major tourist area is the
Whitsundays, where I live. Airlie Beach is the main tourist town well favoured by back packers so a bit of a party town. (I live 20 to 30 mins away on the highway in a small rural town) Of course Airlie is also known for its sailing and has a lot of yachties with the marinas always fairly full usually including a number of super yachts. There is a nice walk that goes from Ailie Beach over boardwalks past a couple of marinas and all the way to Cannonvale Beach. This passes places like Sorrentos restaurant and bar which is a beautiful spot to have a cold one while looking over the Coral Sea.
11. Hamilton Island - Of course the Whitsundays are made of 74 Islands but the most famous is of course Hamilton Island which has a fully develop0ed township with all facilities and travel is by hire of a golf buggy. Hamilton Island also has some good bush walks with some quite steep! Hamilton Island has a famous
race week (yachts) which this year is on from 17th to the 24th of August!
12. Eungella - After the Whitsundays, the next major city is Mackay which is another major sugar growing area and also a hub for mining services servicing the hinterland coal mines. Heading to Eungella you pass through the picturesque Pioneer Valley and then up the Eungella range about 700m up. Eungella has some excellent sites to view Platypus (Broken River) plus some more rainforest walks and the famous Eugella Chalet, a pub that sits on the edge of the range with views straight back down the valley. It also has a hang glider ramp built right in front of the pub. There is some accommodation around Eungella including at Broken River and the Chalet but it can also be done as a day trip from Mackay.
Heading south from Mackay I usually head inland to avoid the traffic on our highway 1 but I will avoid offering further advice as you no doubt also have some places you wish to see which will probably be best accessed by the coast road.
Of course there are many more things to see and do but just thought I'd chuck a couple of suggestions out there.......
Apologies for the word barrage but thought I'd put it out there and you can take from it what you will and anyway I can't help myself when I start ......

When you have an idea when you will be coming this way let me know and hopefully we can meet up and I will shout you a cold one and show you a couple of Lavs out of their natural habitat including an Eagle that has soared well off course. Happy to assist in any way, such as dropping you off at a marina and looking after your car if you decided to go to Hamilton Island
for example. Always a bed here too, so hopefully we are around.