I use the Tetenal kit, and I don't pre-wash. I pre-heat the developer tank though for at least 5 min before starting.
I have not tried to develop more than the recommended number of films, and I would not recommend it - you will prob lose the consistency.
I use tightly closed platic bottles for the mixed liquids, and I can remove the air from them when I close them. I had no problems when using them after 2 months after mixing them, but I really did not want to store them much longer.
Greetings to all