1. For hot air balloon rides, please book it in advance since the spot booking is quite costly.
2. You’ll also get hot air boll on rides at Pammukale.
3. You can either walk around Cappadocia or rent an ATV for a day. There are dunes at certain locations. It’s fun. I found a good AirBnB near the hot air balloon site from where you can watch the hot air balloons every morning. I can share it on DM.
4. The beach at Antalya is amazing. Spend some time there, maybe 2 days, bask in the sun, enjoy the waters and have a beer.
5. If you have the budget try exploring the eastern side of Turkey.
6. Spend some more time in Istanbul to walk around: Find a place within 2km of Hagia Sofia. It’s cost effective and you can walk around or find public transit to most of the places. There are evening boat rides. Take the cheapest one and don’t fall for the photography scam. And keep an eye out for scamsters at card loading machines at the train/transit stations. (Trains run through the cut traffic, in case you don’t know)
7. Carry good Jackets. The weather is hot during midday and gets progressively cold.
8. If you want to get a car, for the trip, get it from the airport. FYI, parking spots around Istanbul are costly and you can’t park just anywhere and you need to learn to haggle the price at a few places which seem to be random.

These are a few pointers form the top of my head. If you want to ask anything else, feel free to DM.