If you use a 10 or even 12 gauge wire your ammeter isn't going to do much of anything. But it's fine, I ran my car like that for years.
You are correct, adding the shunt wire will greatly reduce the load on your bulkhead. A fuse is an important thing to include, but I don't know if I would use the MAX30 in a stock looking engine bay; I would probably go with a fusible link. With that said, I used a newer style fuse, but my setup is way far from stock.
It's probably easiest just to watch the DDG video from a couple weeks ago; he covers just about everything: