Yes to your second question. SME supports virtual domains, and yes you can have seperate email for them. On the email issue, every user on the system is unique. You can not have 2 users named robert, but you could have bob and rob. This is fairly well explained in the SME7 manual that is available in the FAQ section at the left.
On the first question: More information is needed. How is your server configured? Are you behind a router? If behind a router, have you forwared port 21 to your server?
Are you trying to ssh in from a linux or windoze box?
For windows I use Winscp3, which works great. There could be some remote access settings you have missed.