Temp swings aren't really good for the plant, it cause stress. Just get a heater that has a temp set on it so you can keep the temps within a 10 degree window of 70 to 80 all day, that is the best.

As far as soil, go with a stadard potting soil with no nutes. NONE

From my exp. like to use the schutlz liquid dropper feed for veg growth, its more than enough. Start at half strength, move you're way up if the plants like it.

Don't forget about the lights, they are just as important as the soil and feed.