How much developer depends on the developer you're using. I use D76 straight and plan on four 8x10 sheets per quart, or 16 sheets per gallon. For 4 sheets I'd use a quart of D76 in an 8x10 tray with continuous agitation (shuffling through the sheets at the rate of about one pass through the stack every 30 seconds,) but if this is your first time I would process them one at a time to avoid scratches. It's important, I think, to see what can be done before you start trying to improve the process.

It is important to have enough depth of solution to lubricate the sheets well enough to help avoid scratches. I wouldn't use less than a quart of solution in an 8x10 tray, or perhaps three quarts in an 11x14 tray, if I were shuffling through a stack of negatives. I also pre-soak my 8x10 negs in water for a few minutes if I'm processing more than one, so they won't stick together in the developer.

Washing one at a time in a tray with a siphon will do fine. If you want to wash more than one get an 8x10 washer: you're just asking for scratches otherwise.