As disneyhorselover said: "However, my first thought when reading this thread was if you need to ask that many questions about the friend you wanna bring, you might be bringing the wrong one--it should be something to be thrilled for, not worried about!"
I agree. Go with your gut when picking who to travel with. The energy level is important as is the money. In addition to them having the basics (transportation, lodging, food) paid for, is the amount of money they have vs. you going to be an issue? That is, let's say one of you can afford to shop and the other can only window-shop because they don't have a lot of extra $. Are you both going to be ok with that? Can one shop while the other does something else? Or if one wants to shell out extra $ for a special tour, or spa visit or whatever and the other one can't afford it, will that be a problem?
Definitely discuss expectations and finances prior to the trip. Splitting up occasionally might be a good idea, as mentioned before.
Bottom line is whoever you pick should have a really good attitude when adversity strikes. I took a friend one time to DLR on a last-minute trip when another friend had to cancel due to illness. He griped about the cost although one of the tix was given to him for free. He got sick on a ride and had to sit for nearly an hour to feel better (I waited with him because I would've felt like a heel otherwise but it was killing me!). He got tired about 5pm and left me alone the rest of the day - I even let him take the car while I rode the shuttle and I had to wait about 1/2 hour for it. Had to bribe him with a Mickey ice cream bar to get him to ride PP. Seriously...there was no pixie dust on that person and it brought the trip down. Thank goodness it was only two days.
I share that to say - make the right choice because it'll make or break your trip. If you don't know anyone that'll fit the bill, honestly, you can have fun at WDW on your own (well, depending on your personality!). I haven't been to WDW yet but I've been to DLR & DCA several times on my own (just for day trips or
MNSSHP) and the first time I wasn't sure how fun it'd be. Yes, my first pick is definitely to go with family, but I did enjoy going alone...I actually didn't realize how much I could enjoy it by myself! I think that realization was the catalyst that turned me into a Mousejunkie!
Now I'm getting deep so I'll stop. Good luck with your choice...don't be afraid to go solo if necessary and have a great time no matter what!