Would that still let me line up with the wall duct? I guess I need to go to the hardware store and get some ducts so it makes better sense in my head. I'm guessing I'd need to cut them down. I keep thinking if I angle any less than 90 It's impossible to line up with the wall duct which will be sticking out starting... But I'm not smart!

It's a load bearing exterior wall so I'm not sure, beyond my comfort level really. I guess my question is, would only using two 45s still allow me to offset a few inches to the left and then out? That's the part confusing me, the duct cutout in the hood is directly in middle of it ( on top), so I need to start there with duct, go left a few inches, and then connect to the exterior wall vent duct which will be likely at top (inside) of cabinet

From different research I'm not sure the CFM advertised is true CFM so they say to overshoot what you need.. but you're right I don't need 900cfm but it's 4 speed so I'll likely run it much lower.

You're probably right, I figured if I was going to do it may as well future proof myself. The range hood I'm looking at has a 600cfm or 900cfm option. I figured I may as well go with the highest.

I have a gas range, it's 44,000BTUs. Perhaps you're right. The range maxes out at 900cfm but I imagine only having it on level 1/2 most of the time. I could go down to the 600cfm option and use 6 inch. I may or may not still hit the stud but would have to do some cutting to see.