My big reason for going with aluminum is I'm more familiar with those alloys. There's a billion steel alloys out there and I'm not really sure which ones would fit this application.
Re-torqued lug nuts to 75 ft-lbs today
I also found a different solution for the front today - camber bolts. Used some camber bolts to pull the tire away from the strut at the bottom, then used the strut mount to dial the negative camber back in. Worked perfectly and cheaper than spacers.
I'm likely going to pose my second idea to the machine shop sometime this upcoming Wednesday. I'm going to try to have a 10-15mm hub centric spacer, with hub feature made (so I can use my existing hub rings). These will not have studs in them so they will require longer studs (2.5" ARP's should be fine).