1. Document before you decide anything
Note what's visible, take reasonable steps to keep it from spreading, and pull together the home's relevant history.
2. Evaluate the house and site
The install method, flashing plan, sill condition, frame material, glazing package, trim restoration, and how much sun that wall takes matter just as much as the unit you choose.
3. Nail down a written scope
Address prep, protection, materials, access, permitting, testing, cleanup, finish restoration, exclusions, and how change orders are priced.
4. Line providers up against each other
Check credentials first, then weigh how each provider explains their reasoning and where their scope ends — the total is the least informative part.
5. Don't sign off until closeout is confirmed
Make sure testing, cleanup, documentation, and warranty terms are all confirmed, and that you understand what maintenance is left to you.