Wow... lots of questions... takes deep breath :)
if it comes with vista pre installed then Yes, when you get it plug your mouse etc. in and should all work. beware though a lot of modern computers don't have ps2 sockets (the round ones) for keyboards and mice and only support USB ones.
As long as the computer has a wireless card then yes you can connect to to your network if you know the key. I wouldn't recommend it though. It's a desktop so your not likely to move it so why use wireless. Wired is faster, more secure and more stable. use the network cable to connect to your router is a better idea.
Vista comes with windows mail, outlook comes with mocrosoft office, so if you have office and install it you will have outlook and can use that. If not and you do end up using windows mail then it's pretty much the same as outlook to setup. Click tools > accounts and add a new mail account entering both incoming and outgoing mail servers for your ISP and your email address login and password.
When you say seperate hard drive do you mean USB... if so yes just plug in and move the info over.