I check 2x a day for pee/poop. Since I use paper towels I don't really spot clean. I have spare tubs that are always fully cleaned and disinfected. When someone went to the bathroom I just lay down paper towel in the clean tub and throw the snake in with their hide and bowl and spray/wipe the dirty tub.
Water gets changed about every time I feed. Same system as cleaning by using an extra bowl. Slide tub out and feed, snake coils, I pull the dirty bowl and place the clean one in and then wash the dirty one to swap to the next tub.
I feed everyone every 5 - 7 days, just kind of whenever it's convenient for me. They CAN get overweight and you can tell they're starting to get there by whether or not you can see the skin between the scales. A fat snake will have obvious white borders around every scale from their skin stretching. The scales from new sheds should be able to keep up with their growth so if you see skin between them you know you're feeding a bit too much and should either feed less frequently or smaller meals for a few feedings.
I handle whenever I have the time and they're not digesting/shedding.