To explain a little more, question 1:
A subdomain can be use for sub-sections on your web site or actually for a whole new site. It means you can have a subdomain to be called business.mydomain.com and have it redirected to a folder where you have a web site about business.
If you have 4 subdomains it means you can have 4 of those names and redirect them to whatever place on your hosting you want.
Some hosting companies give you more than 1 FTP account because you may have people on your company or co workers to who you assign an FTP account and only give them permissions to upload to a certain folder, you may grant permission to change the files on that folder or only to upload.
Also you can create an FTP account to customers so they can upload large files there instead of sending them by email.
You do not have to do any legal registration in order to make your web site copyrighted, basically if the design was made by you and the content also, you can give permission or not for people to copy the content and design. If you copyright the content means that no one should duplicate your web site or copy parts of it unless you give them permission to do so.
If you have 200 emails is great! you may give email accounts to your friends, create accounts for each of your companies departments, for example firstname.lastname@example.org
, or Support@mydomain.com