I would not recommend leveling up a character for someone else. All of what I have below is far too much work to do if you do not intend to keep the character. Plus all of the ban happy behavior that you will have to deal with. All of that said...

I'm new as well and my situation may help some. I'm leveling a shaman (that I had since vanilla wow) with a death knight. I'm in the mid 70s atm enjoying my casual exploration of northrend. I run both on the same computer without any kind of pip -- I want to "drive" one character and the other will always follow and react for combat. I don't have that yet and spend probably more time tweaking things than actually leveling the characters. By 80 things should be very fluid.

My screen is setup to try to keep as little on the screen as possible. It is in need of much work...because at one point I didn't realize my characters weren't grouped and had to do some quests...twice. Although, I do collection quests with both which isn't too painful.

I use jamba for following, group and some quest stuff. Bartendar4, bindpad, and tons of macros that are highly specific for a dk and shaman. For example, when the deatk knight taunts(dark command then death grip) something, the shaman casts wind shock on it but only if already in combat. If out of combat that same macro will have death grip used instead. I have others thare much more nested with a key to debuff + damage, damage, area effect, ranged, oh shit(ghouls + elementals oh my!), ... Map out what you want them to do and use bindpad/hotbar to make them work. Initially in most of my attack keys the shaman would just assist the dk and cast LB. When I got to 75 I worked in flame shock and lava burst -- big increase in dps of even a restoration spec'd shaman.

I always hated not having a tank or healer at times -- so I have tried to make my setup so that it will allow tanking with the dk and healing with the shaman. So far I've only grouped with my brother's warrior or warlock for some instances. It is very intense trying to do tanking and healing at the same time. I have by no means perfected it and still get overwhelmed at times. I imagine it would be easier if I had a full group...but I want to perfect it a bit before I grab others.

I use keyclone and dedicated a core for each wow instance. I prefer to have all of my letter/chat keys set to be do not pass (however any modifier+letter is broadcasted). I turn off do not pass for login. I do offensive actions with the number keys, healing is with the numpad and focus is set with F1-F5 keys. Heals are setup so that the shaman will heal a target if it is friendly, then heal the focus if friendly, and lasting heal himself. Alt + the healing spell key will force it to heal the shaman regardless. The focus keys are setup to use raid icons as well...I use star for group members and triangle for other focus target so that only one is ever shown. I do not have time to type orders in combat or tell people who I'm healing...basically don't do stupid shit if the star isn't over your head. The triangle is there for hex...but I may take that out since I really like healing with focus. It gets fast health updates with minimal overhead. F6 is the focus target other/triangle key...allows me to heal random people aswell. The F7-F12 keys are multibox stuff like group up, follow, interact target, mount, etc. If the characters ever get separated I hit the pause key and mute all key passing and alt tab as needed between them until they are reunited.

I play on malorne and there isn't too much world pvp. Until 80 it will just be random battlegrounds to test the twitch factor of my setup. I haven't confirmed if there are any other multiboxers on it -- I noticed another guy that looked like one but he never responded to tells. No one seems to mind that I play two characters. I am always amused to see non-80s automatically run from me that are solo. I enjoy hunting them down

Your setup will have to be customized to your needs by you. There really isn't any click and instant mutlibox setup. Planning and implementing it is a major fun factor. I use an in game notepad addon on the dk just to keep track of bugs or features I see a need for while playing. I've spent quite a bit of time lurking and using bits from other people on these forums.