As little as 2L of liquid with RC paper though with fiber paper it may not cover the edges of the print so 3-4L would be better for the developer at least. After the fiber is wet is flattens out.

I use multiple trays and have 6 of them for developer, stop, 1-2 fixers, wash, permawash, toner, drying drip tray.

I've always use tongs in chemicals, and sometimes use two for 16x20. Hands are OK in the wash tray, not fond of gloves.

16x20 looks and is big! It's as big as I can go without doing floor or wall projection. Not sure how I'd handle trays any bigger, 16x20 is already pushing it getting 3 trays on my dev/stop/fix table.