Home page theme settings

Hello everyone,

I am new to MU WordPress and i have 2 questions please:

1- those 100 themes pack, where do i put them exactly ? In the users theme folder or in the main theme folder ? And which one will work best for my main site?

2- on my main home page (my main blog) how can i put the log-in or registration box, list of the blogs or chosen 10 best blogs or last 10 blogs,..things like that , how i can add them on home page and which them you suggest for that ?

Thanks !!