Are expansion joints required when running wire to an outbuilding?
Conduit
Is there any way you can move that east-west pipe north two grids (I'm assuming up is north) so it hugs the house?  That would reduce you to three 90s including the stub-ups.

You need Schedule 80 PVC for the stub-ups at both ends (bottom of vertical curve to conduit body).

Expansion joints, I just don't glue my PVC conduit except where I need to, e.g. within 10' of a stub-up or corner because I don't want it coming apart or moving from pull forces.  You won't keep water out; that's a lost cause.

Speaking of pull forces, make sure that pipe is good-and-buried and tamped down well, before you start pulling. The pull force would much rather move the whole pipe than just the wire.

The conduit body does not count as a 90, because it is accessible.

The stub-ups don't have to be dead vertical. If you're parallel to the building you can use a 45 degree at the bottom of the stub-up and come up the wall at a slant. The conduit body doesn't care. Two 45s like that and an extra-broad 90 underground wouldn't be terrible to pull, given your favor for extra large conduit.  I would use Rigid for the exposed slanted part, because idiots.

If this seems like a lot of digging near the foundation, consider that Rigid conduit only requires a 6&quot; burial depth.  It's hella expensive, but it doesn't look like far, and you can trench it with a garden trowel. The only downside to Rigid is it must be cut and threaded, so it'll take a few runs to a hardware store that cuts and threads pipe (and shoplifters).


By the way, that stuff is all much cheaper at the electrical supply.
When you're at the electrical supply, mention your &quot;thin wall&quot; problem.  I bet the person will disappear in the back and come back with a couple of iron or aluminum 1-1/2&quot; 90 conduit bodies that have nice stubby ends.  That plus a metal &quot;close nipple&quot; and a metal nut, should get it done.
If you can't solve it any other way, I'd thicken the wall in that immediate area with some plywood so the geometry works. Probably help with the conduit entering the ground also.
Wire
I don't know where people get the idea that #2 aluminum is rated for 100A.  Table 310.15(B)(16) plainly states 90A in the 75C column, which you usually get to use. (60C if dealing with UF or NM). I suspect they are stealing the friendly derate from 310.15(B)(7), which is only for whole services not subpanel feeder.
You need #1 aluminum for 100A feeder. (or #3 copper).   That with a #8 copper will fill your Sch 80 conduit to 26% which ain't so bad.  You can use #6 aluminum for your ground, as long as it's insulated.  Only copper can be bare in a wet location.
THWN or XHHW wire can't just be loosy-goosy flopping around in your walls. But it sounds like you are running straight out the back of the panel via a conduit body into conduit runs, then back out the same way.  That is all conduit or raceway which is fine.