Not sure what the open pipe is for but it's surely quite low and I wouldn't leave it uncovered like that, just inviting a problem down the road. Maybe something like this.
Sweeps or (2) 45's are less restrictive thus theoricaly reducing head pressure. Can you quantify it? Probably not unless you had to identical systems side by side. It's more expensive and takes more space. I personally use sweeps and or 45's. That is my opinion of course yours may vary
Not only can I quantify my flow, I made a gif of it clearing the 40ft wall into a moderate wind.
But yeah. Some 90s won't reduce the flow enough to care. It'll still flow for days. I was happy they were using sweeps on the build, but i had way bigger fish to fry if they weren't.
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