How much ventilation?

[ws450r]

I have a basement that is unfinished with a garage in it. There are no seperating walls, it is one open space approx. 600 square feet. I am replacing some of the basement walls this spring to allow them to be straight again. The ac/furnace unit is in the middle of the floor along with the water heater next to it. My problem is it doesn't hold the heat very well, and I can get the upstairs nice and warm before I go to bed, turn it down to 60, and at 2-3 in the morning it will start to kick on and run for awhile, shut off for a few minutes, and kick on again. Like a continuous cycle. After I replace the walls, I am planning on building a wall seperating the basement in half, along with enclosing the furnace, build some walls around the outside foundation and insulate them, along with some sheet insulation where the garage part is. Hopefully this cures some How much ventilation should I allow for this. My parents have a sliding door with the slats in it for theirs, and am wondering if this would be enough? Also, how much would a thermostat upgrade do so it doesn't kick on and off as much?

Sorry for all the information....but I am looking for a lot of it.