Oh, I don't think the game is really playable in a continuous way (that is, without moving to a different town all the time) without several NRAAS mods installed, especially several of the bug-fixing ones. I hope you use at least Error Trap and Debug Enabler. I think Master Controller is more or less indispensable. I also recommend the cheat module for Master Controller. Despite the name, it's really useful in many situations.
Dreamer is also nice, for "on the fly" switching of families with a right-click. At some point, I found myself using almost all of the NRAAS mods.
Edit: Just saw your edit. That "pixel weirdness" is probably the usually invisible oval mat the game places where two sims interact which each other. Sometimes, the game forgets to delete that one. I usually get rid of it with a radius purge (size 1) with Debug Enabler. You can also just reset lots with MC by the way, if you don't want to do the whole town.