At how many days/weeks is considered the end of seedling stage, how long should veg really last, and third what rh and temps should the tent

Some say 2 weeks for seedlings, others say 3 weeks. Some consider Veg part of the seedling stage so count the first day the plant sprouts as day 1 of veg. Veg with photoperiod plants can last as long as you want. If you want a small plant, flip to flower after 30-40 days. If you want a big plant then veg longer. Some growers keep their plants in veg for years specifically to take clones from them (mother plants).

Temp about 82-83F leaf surface temperature (if you're getting exact). Or 70-80F for HID lights and 75-85F for LED lights. Other growers may have different suggestions. Safe RH in veg is 40-60%. For optimal levels, google VPD chart so you can see RH according to temperature. Although, I don't recommend that to beginners.