Fresh 727 first start up

Hey guys, I finally got another 727 transmission for my RamCharger and rebuilt it with a stock rebuild kit.
I filled the converter with fluid before putting the trans in the truck.
Now I’m wondering how much fluid I should put in it before I start the engine for the first time. I’m assuming it should be in neutral when I start it, right?
Any tips on what I should do?
This is my first transmission rebuild.
Also, how do you recommend cleaning out metal contaminated fluid from the trans cooler in the radiator?
Thanks.