Welcome to the Mamiya MF family (or soon to be). I have a 1000s so my comments will be brief since our bodies are different, but Mamiya is a blast bc like said above you can make it work for you so easy, lots of options! Some Apug'r made a web based Mamiya accessories/compatibility tool, can't remember the link, but it is a nice site (chime in owner if your watching).
Anyway re the 80mm 1.9, I own that and love it. It is the fastest MF lens ever made, quite costly (generly $300+ or so on eBay/KEH). If you want to shoot wide open with about the thinnest DOF go for it, I love it, you have like +/- one inch to nail focus! It's like using a f .95 Noctilux. When you nail it, it is a joy but be prepared to roll thru more film. But it is costly so if money is a consideration the 2.8 will work just stellar too, is 1 stop worth a few $hundred more to you? Only you know that answer. I only have 1 lens, but we all photograph different.
I have a metered prism and WLF, both serve me well for what it's worth.