Permits for Adding a MIL Unit

[Kendal Keyes]

We just closed on our first house in Lynnwood, WA (unincorporated Snohomish County). It is a bi-level, and in order to make it work financially, we are planning to "house hack" and rent the downstairs to friends who are already lined up. We will live upstairs. We will be adding a small kitchen to the downstairs to make it a complete separate living space (just sharing utilities). The house meets all the requirements to add an "Attached Dwelling Unit". I'm worried about my timeline because our tenants need to move in in just under 2 months. My questions:

1. What could be the possible ramifications for NOT getting a building permit from the county, or getting one after the construction is complete?

2. We plan to do most of the work ourselves, with the exception of hiring out rough-in for plumbing and electrical. Will I run into hiring issues if my permits art not lined up ahead of time?

Thanks in advance!