I think a lot of your questions have been answered, but I have a few comments based on my gameplay.
My spellcaster sims took their daughter (born before they became spellcasters and thus without a magical bloodline) to the magic world multiple times. She usually spent her time fishing or socializing with the sages like a nerdy child who got along better with adults would do. It's easy to have sims make mac and cheese in one of the cauldrons and there are benches to nap on so she could pretty much take care of herself while they were there, even with the original lots. She's currently a YA having a fling with Morgyn and also with the scarecrow in her mother's garden.
I made a different household with one sim focused on each type of magic, and I got bored with the untamed and mischief ones. Mostly because their low level spells are mostly useful for causing problems, either harassing other sims or setting things on fire, and that doesn't fit my primary playstyle. Practical magic progresses faster for me because their spells are useful so I cast them more often. I recommend a focus on practical magic or a mixed focus, unless you really like pranks or fires.
Curses are super fun, for me. I like a little chaos in my games, but not random death so much, so curses are pretty perfect. My one sim had three when I left her last - she was green and warty, her spells often failed, and she randomly burst into laughter (which was contagious). It was the most fun session I had playing a spellcaster. I can't tell you if they resolve on their own while you play other households yet, because I have a large rotation and haven't gotten back there. But even if they do they add a fun element while they last.
