That is so sweet that you're running into tons of lures. Did you catch any cool ones by the dock? Right around where I live I usually catch the common ones, but when I go to the beach there are a bunch of different ones.
If you leave your Pokemon at a gym, they'll stay there until they get defeated - then they just pop back up on your list. When you click on a gym that's on your team, there's a little icon on the bottom left corner that shows up if there's space for another Pokemon there - then you can choose one to drop off.
with any creative arts motivation goes up and down all the time, i have a friend who's amazing - he draws all day, everyday - it's amazing how some people just have the need to draw or paint and can be so prolific. i haven't played miitomo for a while - i actually just looked at it today to see what was new, it looks like they've updated a few things but nothing interesting enough to get me hooked