If I turn on Village trade reset, and their maximum level Master reached and all trade finish, do they become permanently cannot trade anymore? thx

Trade resets doesn't affect the villager's level. Everytime they restock (which is usually every in game day) they will have their trades changed.

In vanilla, do trader never change the trades forever?

Correct. Restocking only unblocks blocked trades in vanilla.

No problem. Still worth to enable the option as we sometimes want to stay in 1 village and get bored with same item sold by trader but dont want to travel whole map just to find another trader. Thank you very much!

Is it possible to make reset trade without limiting 1 trade per level?

increasing the amount of simultanious trades lowers rarity too much,
as you have lots of trades and they all reshuffle every 5minutes at least (assuming the villiger is working).
there is no option to increase the trade count and i'll not be adding one