I startet mine in cup`s in the window shelf, like a month before I planed to set em outside (when spring hit us and night frost was history)
so your right on track there, also with the soil, tho make sure it hold a lot of perlite and maybe some lega nuts/stones, but most important, make sure your pots have nice drain holes in the bottom, so they don't drawn if you get heavy rain and is`t there to safe em inside
most importent when choosing soil beside getting it airy and light for the roots is PH value, some cheap "supermarkets" soils keep to much peetmoss and is to acid with a PH under 6, look at the Bag, weed need a PH between 6 and 7 a good thing to add/mix in to a acid soil or old/used or any soil for that matter is Lime, Dolomite Lime, both help you to keep the PH neutral and add calcium, Dolomite Lime can be found at most garden centers and is relative cheap, a Cup mix in to a Bag of soil can do a lot for your plant`s
and about fertilizer, a good soil keep a good amount of food, and will in most cases have enough for the fist 3-4 weeks wile your plants is small and don't need as much to grow, once they get a few set`s of "real" leaf`s and have used up most of whats in the soil you can start adding it, maybe every other watering, but start out low, maybe 1/4 strength of what the bottle say and work your way up wile the plants grow and demand more, fist when you have big plants you might be able to add max, but remember, less is more, so to speak, better to be a little on the low then to burn em, early on in the vegetive stages they will need food with high Nitrogen (fist number on the bottle NPK) when it begin to flower it will begin to need less N and more P and some K, do some research