26.520.000 XP to level 100. Even if you complete the game using the best badge combination, you would still have to complete a level 6000x or complete 1000 daily puzzles...
Important hint: if you plan to reach level 100, wear the XP combination (see my previous comment), use the Pray badge instead of the Animal in general levels, EVEN IN JUNK LEVELS! You can get gold naturally, just focus on XP.
IMPORTANT PRIZE: Finish X Science related puzzles. I don't know how many, but I got it after finishing Microscope (easy, page 7, 2th puzzle) this prize will give you a FREE BADGE SLOT!!!
IMPORTANT PRIZES: visit shop 100x and you get 100.000 gold. Retry 200x = 30.000 gold. 50000 xmark = 40.000 gold. there's a lot of prizes that will help you to get gold fast, so check the stats and try to figure it out!