A new opener kit looks simple in the box: rail, motor head, a few brackets, a wiring harness. What the instructions don't cover is what's already on your header. If you're working on a house from the early '90s building wave that's common here, there's a real chance the existing bracket doesn't match the new unit's mounting pattern, and the manual assumes you're starting from bare wood. Climbing a ladder to wrestle a 20-pound motor head into a rail while also fighting a mismatched bracket is where most DIY opener jobs go sideways - not the wiring, the mounting. If your bracket and header look original and solid, a DIY install on a straightforward door isn't unreasonable. If anything up there looks bent, cracked, or like it's been patched before, that's not a project to learn on.