It's fine to prime, and to paint ceilings, but sanding is a dirty, dusty job. The dust will get on your walls. The sander handle may mark walls. Stain can splash onto walls. FWIW: You can paint over stain, but not the reverse.

You did a great job! If you want, get some antique glaze, it's brown, and dab on some of the glaze here and there. Will add another layer of depth, and because it's glaze, will be very subtle. I'd go with a chunkier lamp. The legs on the console are a bit thin for Tuscan, so maybe you could find some gorgeous textile and use it as a table drape? Some purple, yellow, and olive green would be perfect. I wouldn't add any vines, but bring in a wooden box or a ceramic bowl to hold keys, mail, etc. Not the wicker basket. Tuscan is sumptuous and abundant, you've definitely nailed the wall treatment, and that mirror is awesome.

Should make no difference

Being a paint contractor I deal with lead all the time. I think people do get carried away with the dangers of lead. Im sure your walls and ceiling where originally painted with lead paint, as well as your exterior siding. As long as you have a layer or in your case multiple layers of paint covering the lead base layer, it is contained at that point. It really cant hurt anything at that point. If it was me I would replace all the trim just because its a pretty easy fix considering. That way you wont have to worry about that part again. It will also look a lot better. The MDF baseboard works good, and paints well if your gonna paint it, and is rather inexpensive. Good luck!