Questions from a beginner (Gym)

Recently started the gym, I’ve done my fair share of research but I am still curious about some things!

1. I am a rather skinny girl, and I’m trying to build lean muscle instead of fully bulking up. How much extra above my TDEE should I eat?

2. Does it take longer to build muscle when lean bulking instead of going ”all-in”?

3. Do I have an advantage with newbie gains if I already have underlying muscle from running and pilates? I’m stronger than the average but I don’t have a lot of visible muscle. Curious as to if this muscle is waiting to ”pop out” now that I am strength training.

4. When strength training, I go until failure. My 12th rep I usually collapse by, if I’m even able to complete it at all. However, I don’t feel a lot of burn, my legs just overall get tired until they give in (e.g. in RDLS). Am I still building muscle or am I doing something wrong? My muscles also don’t burn after a completed workout, my legs are just incredibly tired. (Maybe they aren’t supposed to, I’ve just always assumed they should…)

I think that’s all of my questions, thanks in advance!