You've got more than enough computer to run two accounts. For targeting, on your slave character you pretty much have to use macros:

/assist (main toon's name)
/cast Frostbolt

for pretty much any spell on your slave. That's the simplest way to do it. When you start getting into higher levels (more spells) and if you add toons later, I would highly recommend the Focusless, Leaderless, Targetless setup and KeyClone.