1. Document, then contain the problem
Note the symptoms, prevent further damage where you safely can, and gather any relevant history on the home.
2. Assess the house and the lot
What's underneath, sheathing condition, the house wrap, flashing at every window, and clearances, has more to do with long-term performance than the siding material itself.
3. Put the scope in writing
Preparation, protection, materials, access, permits, testing, cleanup, finish restoration, exclusions, and change-order terms all belong in writing.
4. Line up the proposals
Verify credentials, then compare each proposal's reasoning and boundaries, not just its total.
5. Confirm the closeout
Testing, cleanup, documentation, warranties, and ongoing maintenance responsibilities should all be confirmed before calling it done.