Is it appropriate to contact prof before I accept to talk about the projects again ?
Absolutely, yes. This is particularly useful if you are joining a PhD program.
You can always email them, maybe even asking to schedule a meeting so that you can discuss your interests with them, and possible directions for your research. You lose nothing by asking. Make it clear that you haven't accepted the offer yet and would like to have a clearer idea of what you might work on, before making a decision.
Don't necessarily expect an immediate reply, however. Professors are extremely busy, and it could easily take a week or more for them to get back to you.