OpenMediaVault NAS / General questions

Hi,

I would like to set up a NAS server for mainly : data storage, ftp server, multimedia streaming...maybe a web server.

So I read for hours about FreeNAS, Ubuntu Server etc and OpenMediaVault seems to be the one that is promising, even if it has not yet a large community around it. However I'd like to give it a try.
So since it's based upon Debian, I've got some questions. I'm starting in the Linux and networking fields so the answers of some of my questions may be obvious for some of you and I'm sorry for that.

So,

1) When installing OMV, can we do it over an existing distrib or it has to be installed like any other distrib?
2) When it is installed, can we access all the services via SSH or things have to be done via web GUI?
3) Can I access remotely via SSH and start a P2P download (or any download) to the server for instance?
4) Why go for an all in one package instead of installing services separately to do the job (samba, ftp etc.)

Thanks for your help.

_{Thanks ryecoaaron for your quick reply.}

Your answers were straight to the point and I hope that every thing's gonna go well.

Hi,

I'm gathering the hardware intel to build the NAS and I've been thinking : is it necessary to have the os installed on a ssd or it is a waste of money?

Thanks