A few thoughts from me:
5.0 or 6% (depending on the manufacturer) should be fine.
Most prefer the long tube over the coiled kind. The tubes come in two sizes: T8 (fatter) or T5 (skinnier). Make sure to buy the right bulb size for your fixture.
You may want a double fixture so you can add a plant grow light. It made a big difference for me, but I have a very large cage (6-ft tall).
My experience with the Reptisun 5.0 vs the Arcadia 6% bulbs is that the quality of light from the Arcadia bulbs seems much nicer - brighter and better color rendering.
The UV bulb produces very little heat - you need a separate basking light. Use a standard house bulb (or you can get a halogen reptile basking lamp) and adjust the basking spot vertically to get the right temperature. Don't use a red light.
I first bought the cheap Zoomed T8 fixture and later upgraded to the Light Your Reptiles T5 fixture. LYR is very nice quality. If you can afford something a little nicer than pet-store brand, do it.
All lights go off at night. All of them. Unless it drops into the 50s or below, you chameleon will be fine. A temperature drop at night is normal and healthy.
Good luck!