Newbie help and advice

Hi Everyone, I joined wpmuudev a few days ago with a plan and have suddenly gone into panic and fear mode and feel completely lost. My goal is to set up a couple of content led community niche sites enabling users to set up their own sites around the niche to create a niche network. Before I signed up I read the support manuals and psek was recommended for hosting but when I've checked out the forum and searched the term 'hosting', I notice that people are using all sorts of hosting companies so I don't know what to do. I also don't know which theme to use.. Had a sudden loss of confidence and maybe just need some reassurance I'm on the right track. Any advice, suggestions would be welcome. Thanks Alison