As far as tips...if you've already made you TS ADRs you can go to allearsnet and look at the menus for those restaurants and get a rough idea of what the cost would be and figure 20% tip. We will be 4 people (3 adults, 1child) and I figure depending upon restaurant it will be around $30 per sitdown for tip. As far as maid service you can figure about $5.00 per day or whatever you think best.
You can get gift cards for souveniers that will give everyone limits which is helpful, but I find the real problem to figure out are all those "little extras". You're on vacation, you're in Disney, you're in a good mood so...things like light up toys from the carts when waiting for night time fireworks or parades seem like a good idea to buy. Penny press machines look like fun and you start pressing pennies, character autographs...let's get an autograph book! Sitting on a hot sidewalk waiting for the afternoon parade and those mickey bars look REALLY good, but you've already used a snack credit that day...it's so hard to tell what you will spend your money on that you didn't plan for. You get one of those famous Florida thunderstorms and decide to buy ponchos...I keep smelling popcorn and have to have some!
So it all depends on how much restraint you have...Disney is a wonderful merchandiser with ALOT of attractive merchandise to sell. DS loves having his caracture drawn when we're there - last year he wanted 2! And our first year there I had to get one of those silhouette cuttings of my son on his first Disney trip.
So if you have a budget you neet to stick to, then do it...and you will be fine. Or be resigned to the fact you may get pulled into the Disney vortex of gifts and overspend a bit, but hey, you're on vacation and that's what it's all about.