Abj, cutting your rosemary won't hurt it...cutting the terminal ends encourages the lateral buds to develope...in other words, it gets bushier. Give it a shot of feed, let it get dry between waterings, but don't let it STAY dry. I don't know how big your plant is, but that's a pretty big pot. Rosemary does best when it's a little pot bound. If there's too much extra dirt, it tends to get root rot.
The more you cut on your basil, the better it will grow. When it blooms, be sure to cut those back so it won't go to seed. It doesn't need a bigger pot...just keep it cut back, fed, and water when dry.
Heat, a west window will be great for herbs.
Remember that plants are living things, like baby chickens. They need the right amount of food, water and a place to grow. Too much water and they drown. Too little and they die of thirst. Plants with big soft leaves, like basil, take more water because they have more leaf surface for transpiration. Ones with hard little leaves, like rosemary or thyme, use less water.
The more water a plant uses, the more feed it needs, as all that watering leaches the nutrients out of the potting mix.
About potting mix...NEVER, NEVER, NEVER try to save money by buying the cheap stuff. Your plants will sit still at best. I used to make my own, mixing peat moss, vermiculite, perlite, lime and slow release fertilizer. Now I buy Miracle Gro...it's the most like my "homemade" that I've found.
I hope this helps...any questions you all might have, I'll be glad to answer if I can. After 22 years in the business, I still don't know everything.