i would suggest the rm 1000 i, it cost less and should easily handle all your 5 gpu even 6 are possible, and gpu ram does matter yes, on some algo, there are some algo that you can't mine without 8 gb like the one for zero, a coin with a special forked algo, harder parameters
Sadly, from where i am, its really hard and expensive to get PSU and other stuff. AX1200i and Hx1200 are my only option.
i will go with strix rx 580 8gb then