A Couple Questions from a Noob

I'm new to growing. I have a couple plants going, planted them 16 days ago, they're looking good. I have some questions:

I grow in a building that doesn't have heat on inside of it (and I live in a place where it gets cold in the winter). My plants are in a grow room which is 4 2x4's covered by black plastic. Will a small heater help in my room? Any other ideas to help keep heat in the room?

Also the plants I have are under a 4 foot floro which has 2 4 foot lights... will this do until I want to flower them and put them under my 600w hps?

I also have some plants outside, but I started them late in the year... I want to keep them alive for as long as possible... Will a frost harm the bud at all?

I appreciate any advice!

yes the frost will turn your buds into a pot slushy. remember if you use a heater it shouldn't put out any light during the dark period if it glows red at all it will turn them to seed