Running power to an outside shed
Use conduit

Putting in some 2" schedule 80 PVC now is a cheap investment compared to having to dig up a busted cable to replace it.

Torque your lugs to spec!

Get an inch-pound torque wrench and torque your breaker and panelboard lugs to manufacturer's spec.  This is a new requirement with the 2017 NEC, spelled out in 110.14(D), and simply good practice anyway, especially with aluminum (which is a bit more sensitive to torques than copper is).

Make sure the outbuilding is grounded

Since you have a feeder to a subpanel at the outbuilding, you'll need to put in a ground electrode at the outbuilding and wire it to the ground bar in the subpanel, which will be separate from the neutral bar, by the way.  (Make sure to pull that bonding screw or strap in the new subpanel!)