Welcome to the forums, rozeltf
Note, if you pick a domain and register,
and later have to use another,
just open a help desk ticket (link at top of page)
to ask to have your domain changed.
If you get a reseller account with a new domain name
you can have the techs move your current account into your reseller account.
When moved it will have the same space and bandwidth as it now has.
So create a new package for it and then upgrade/downgrade it to use the new package, so it wont take up so much space.
I think you can have addon domains which use a folder.
But they will resolve to the folder.
I did this with one of my reseller accounts to see it work,
but not the main account.