Xe, People are doing it now.
Welcome to the site, Xsd. A note that you might want to change your name at some point in the future, as your current name makes you look like a spambot.
As for the multi-PC question. Several People on the site have multiple "Main" characters one a single account (such as Syren and myself), while many, Many other separate their PC characters by account. As for interaction. I have three PC characters: Z'har Dizen (know to many as The Admiral), Aya, and Resi Sithbane. Z'har and Aya often work together and help each other (as Aya is Z'har's daughter), while Resi is unaware of the other two (but due to the current story-line "SL" I'm in, will soon be trying to kill them both). The big important rule to remember is "One Fleet, One Army" per account. Those troops and ships can be divided up any way that you see fit, but you can't have more than that. In my case, Resi is a jedi knight (and a relatively new one at that) and so doesn't have any ships or troops at his command (save for a single unarmed freighter he uses for transport). Meanwhile, Z'har earned his nickname the hard way, and controls the bulk of the account's army and fleet (though Aya occasionally takes command of them when he is busy elsewhere).