Sure you can. You may not get anywhere successful with a free subdomain (eg. free subdomain from hosting site), but a subdomain can still be successful.
Should I start out with .info and then in a year get a .com? Also, what is up with Whois information. I don't really want stalkers finding out where I live by doing a quick search.
I would recommend going straight to your domain you want. If you can't afford a .com just yet, wait until you can or attempt to find some way on acquiring the funds. If you have your site/community on a .info domain and in a years time you switch to a .com you will lose the brand you originally built up. Although you will transfer PR juice and traffic through a 301 redirect from the .info to the .com, it's always better to start out on top.
Plus, if you use an .info domain, you run the risk in someone snapping up the .com before you and competing with you directly.
It's for contacting purposes, your domain ownership is like leasing a rental car. If something breaks, you'll be contacted (a really awful metaphor but you get the idea 😉). It basically helps protect the stability and security of the Internet as a whole, with network administrators, ISPs, hosts with contact data for domain owners/administrators. Also used to see what the status is of the domain.
If you find a domain which sounds good for your forum, you should buy it right away since someone else might register the domain especially if it is a .com, .org, or .net in the future.