CRM/Data Capture

I am in need of some advice/help please if anyone has time.
I have a website https://www.lifeafterlondon.com. It is made up of forums (through S2Member) and static pages. At the moment I save all the details of those who register on a excel spread sheet because the S2Member info doesn’t store all that I need. However, we are growing our database and need to do more with it, direct mailings, emails etc and we need to follow whether someone has posted on the forums or not, and various bits of information. Is there a way of doing this within the site or should I be looking at CRM and if so can it be integrated to ensure we capture all their activity on the site once they are registered with us.
Would so appreciate help on this before we proceed with an expensive mistake!
Thanks