Can you combine them into larger pots? Absolutely! The biggest thing to keep in mind is making sure you're not overcrowding a pot. The plants should (at full-size) be cozy with each other but not crowding each other out, and the edges of the plants should not extend beyond the edges of the pot (unless you have some kind of trailing plant, but I can't think of any herbs like that).
What herbs grow best together if you can combine them? Oregano, sage, and basil grow great together. I am not sure about other combinations but there are definitely some great combinations and some you'd want to avoid! At least, with vegetables that's true, I haven't tried it with herbs. Also...resist the impulse to buy a rosemary plant unless you have space for it outside...they grow into HUGE bushes! And by huge I mean six feet tall and across, easy!

Plus a very little rosemary goes a very long way lol.
Would it just be better if I grew them in separate pots? Just depends on your preference, I guess. If you do have several herb pots, I'd get a wooden tray of some kind so you can take them all out into the sunshine and in at the same time instead of one at a time.
Edit: also, keep in mind where you will put the plants. If they're going to be indoors all the time, then a south-facing window or some kind of grow-lights is a MUST. Otherwise your plants will not do very well. Also, some plants are annuals and will need re-planting/re-seeding/re-purchasing each year (chives, for instance, if I recall right), some are bi-annual (fennel) and some are perennials and will last as long as you take care of them.
Good luck!
-----signature-----
There are no automatic doors, just very polite ninjas