Advice on Trip to Turkey/Istanbul

Hi

I will be going to Istanbul for 3.5 days, arrive Sat morning At 10:15
am and leave on Tuesday at 7:00 pm. Will be there this Saturday
actually.

Right now I was planning to spend all the time in Istanbul but was also
thinking if a trip to Cappadocia for a day would be worthwhile.
(ideally 1 day there)

Given the tight schedule would have to leave Sunday night and return
either Tuesday morning/early afternoon.

What are some thoughts on whether I should spend all time in Istanbul
or if a short trip or even day trip to Cappadocia is possible.? Is bus
or train an option, I can fly to Kayseri but is a bit expensive and
drive to airport from Ulus where I will be staying will also add to
cost.

I do tend to do a lot while on vacaition and also not sure when I will
return to Turkey/Istanbul, my first trip there.

PS. Any cheap reasonably quick way to get from Ataturk airport to Ulus
(near Akmerkez mall).

Thanks a lot

Shriram