Yeah Gadget was a new tsum made for the coloring book missions (which are always there). Designed for new players. Ursula is also a good coin farmer but all the tsums are better at higher skill levels. You won't really see a difference until level 4.
Yes 100k coins from one play. Again thats rare but sometimes it throws you a few extra thousand. Always use the coin bonus! You're at a decent coin haul to be using it :)