It is A LOT easier than you think to play 24 tables. Just work your way up and find a good setup. Stacking tables makes it very easy, with one decision presented at a time. It also lets you play all 24 on, for instance, a low-res laptop monitor (what I use). You will find that most of the decisions are easy folds, leaving you multiple seconds for closer decisions. This is really only possible on PokerStars, as the software will automatically pop up the table that needs the most attention and dismiss the table to the back of the queue as soon as you make an action.
The concierge service, to the best of my understanding, works as follows:
You send pokerstars one or more receipts for items that you purchased. These receipts must total at least $500. With the exception of select items (credit card payments are listed as examples of rejected purchases), they will credit you with the total value of the receipts at the expense of 62 points per dollar from your account.