1. Yes, but there are plenty of free webhosts. Currently, I'm using zymic for two different websites I've created (see
Matthew Vita and
Welcome to the C.E.R.T.A website!). You can get free domains from
CO.CC - Free Domain name registration + Free DNS service. and other sites such as openDNS
2. phpBB is a free software that's pretty decent for forums. If you go with phpBB, you might want to look into beefing up the security of it. I added a plugin that adds a human question to the registration and haven't gotten a bot signup since.
3.If you look through the files of the theme, you should be able to modify anything, really, as long as you keep the theme creator's info on it.
Also, if wordpress is hosting the blog, you won't need to worry about 1 and 2, as it will only be a blog. *HOWEVER* if you just downloaded wordpress's software for use on your own server, than you'll need to set up everything using mySQL and you'll need your own web host for that stuff.