Your electrical setup is very similar to mine that I'm currently working on. I installed a 100A sub panel on the back of my house to feed three Pioneer mini-splits. I ran three, 4awg copper THHN wires (hot, hot, neutral) and one 8awg copper THHN wire (ground) from the main panel to the sub panel in 1" PVC conduit. 4awg copper is good for 80a (arguably 90a too) but I only used a 60a breaker on it because 80a GE breakers are $80 and 60a GE breakers are $15, and I will only have 50a worth of breakers in the sub panel. But the wire is there if I ever need another 20a in that panel. Also, for whatever reason, 4awg copper THHN was 2 cents cheaper per foot than 6awg at Lowe's.
I was told by a veteran electrician friend not to use aluminum wire. He said you can per code and ampacity if you upsize the wire correctly, but he doesn't recommend it. He did say that if I went with aluminum to use lots of Nolox on each end of every wire. I took his suggestion and used copper though. It was good I did because it turned out that 4awg is the largest wire that would fit into the neutral bus bar on my main panel. No idea how I would have fit a larger wire on there. A lot of people do use 2-2-2-4 aluminum wire for sub panels in shops as it keeps costs down, especially over longer runs. I only had to go 23 feet though.
If you use metal EMT conduit you can use the conduit as your ground and eliminate the ground wire. You just have to make sure the conduit stays firmly connected it's entire life or you could loose your ground connection. I didn't want to deal with that, or potential rust (I live in Florida and my conduit is outside) so I used PVC and a ground wire. But you could definitely do that inside a shop if you wanted to. However, if you're set on the 2-2-2-4 aluminum wire, the ground wire is already in there and PVC conduit is easier to work with.
The 4awg THHN I used is $1.52/ft at Lowes. The 8awg ground wire is $0.97/ft. One inch conduit will fit all that or you could upsize to 1-1/4" conduit for an easier pull. If you do use 2-2-2-4 aluminum you'll need at least 1-1/4" conduit. If you have more than 360 degrees of elbows/turns/bends you'll need to put a conduit body somewhere in the middle to break it up, one for easier pulling and two, I think code says no more than 360 degrees of bends between accesses. That's all I can think of at the moment.
. That will be done later.
