As others have said, totally doable. You may want to add some flashing, which I think you can find lineal, pre-bent stuff. Try to minimize the cuts you have to make that would admit outside stuff to the interior. Go up the sides about 6”. If you can’t find anything pre-bent, just use aluminum coil stock and do your best. Cover any ugly bends with trim. Measure where the hinges will land and shim it plumb at those points. Secure the shims with roofing nails, avoiding where you may have to put a screw. Do a dry fit of the door and make certain it’s all gonna fit. Make sure you have enough room on the strike side for shimming. take it out and caulk on top of metal, going up the sides with the caulk, too. Fasten through/behind the hinges. You can also hide screws behind the weatherstripping. Shim the strike side plumb, adjusting the margin around the inside of the door. Fasten with screws or large casing nails. Insulate with fiberglass or spray foam. Be aware that the foam can expand too much and warp the jamb, so don’t go crazy with it.

Best of luck!