how much yeast for starter

So i recently washed yeast for the first time and ended up only getting 3 mason jars that have settled out with a thin layer of yeast on the bottom. I know I could make multiple starters to build this culture up, but I reall don't care to go through that much effort. If I'm going to make a starter, should I use more than one of the jars? (fyi, this isn't the greatest of pictures. the yeast on the bottom is nice and healthy look, despite how the pic looks.)

If you can decant all the yeast and pitch into an appropriate amount of dme, then use what you have. I would suggest visiting here for details (or another suitable online yeast calculator).

I think you're fine to go with a 1qt starter(with stirplate) or 1.5qt starter(without stirplate) just from eyeballing your yeast count. For comparison sake, here's a before and after of a starter I did from a batch of washed US-05. The 1qt jar on the left is the volume of yeast I started with, the 2qt jar on the right is what I ended up with. Final cell count calculated at roughly 280b, plenty for pitching.

is there a count on how the cell count going into a starter? I've only ever made starters from WLP vials, never from washed yeast. Say i'm shooting for a starter with 180b cells (for a 1.050 wort), how many cells need to go into that 1L starter.

In general, your starter volume is more important than your starting cell count. So long as you keep the yeast in suspension(if you don't have a stirplate, just give the vessel a good shake every couple of hours), they'll continue to reproduce until they have the right numbers to process the sugars around them. If your starting count is a bit low, it might take an extra day or so to get to your ideal number, but it will still get there. For 150-200b pitching rates, a 1L starter is probably about right just to be on the safe side.

So long as you've got at least 10mL(about an 1/8th of an inch in a 1quart mason jar) of yeast solids on the bottom of your storage vessel, you've got plenty of washed yeast to make a 1L starter.

is there a count on how the cell count going into a starter? I've only ever made starters from WLP vials, never from washed yeast. Say i'm shooting for a starter with 180b cells (for a 1.050 wort), how many cells need to go into that 1L starter.
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Calculators like MrMalty and YeastCalc will work all that out for you and it depends on the AGE of the yeast.