Lotsa options, but all my window sill grows have sucked to the point that they were a complete waste of time. If it is your only option, you will get weed, but you would be better off by far just buying some weed when you consider all the time invested for 1/8 oz. I'm not trying to discourage you, that's just been my experience without fail. Others report this as well.

I like to change to budding nutes gradually over 2 feedings after going to flower. If you are in a big hurry for them to start flowering, then yes you can move them to a flowering schedule every day. I wouldn't bother though, unless as I say, you are jonesing or something. I don't use Calmag during flowering, but I do sometimes toss in a little Liquid Karma.

You are putting the cart before the horse a little. All the good food in the world won't make a bit of difference (or at least a noteworthy difference) if you don't get some descent light on them. The absolute best thing you could do for them is put some bluish color CFLs on them (daylight, cool, or 5700-6500K). They're already getting some red light from the sun, but if not much (like if they're on the North side of your house) you should have some reddish lights on them too (warm or 2500-3000K).