Awesome and kudos! I take it this is a kit and if so, take your time and if you have any questions, fire away!
I also would have suggested the metal arm but also, do yourself a favor and address the need for one upgrade... the idler. The stock unit has NO bearings or even bushings! The plastic wheel just rides on the pot metal shaft and eventually will start to become loose and misaligned.
There are several ways to go with this, and of course, money spent on it from just over 100 bucks with Daryl's absolutely beautiful aluminum kit to the Tamiya design OR, do it your self. I don't know if Impact's kit is still available, but at least all of these have bearings and if you're going to battle with this Sherman... GET ONE!
Of course some metal shielded bearings (or the sealed design) for the road wheels would be nice as the kits bushings are NOT shielded and dirt and debris will accelerate their wear.
Like I said, any questions you have feel free to ask here or ME in a PM. I have built 3 so far and have many in the fire too.
Jeff