Shopping for a house in Tacoma WA

[Adam Hanson]

Hey all, 

 I am currently shopping for my first deal in Tacoma WA, and I have a plan for our first "house hack" that I wanted to see if it is doable/legal. 

We are looking for a fixer 1500-200 sq ft (Ill be doing a large portion of the rehab myself excluding electric/plumbing) that we could turn into 2 separate units by adding a second small kitchen and potentially extra bathroom, and renting out the second unit, along with converting a detached garage into a vacation rental we would self manage, while staying in the first unit for the first year to fit the FHA loan.

My questions are for the lawyers and contractors in the area:

1. Is it legal/ what paperwork do I need to create a second unit?

2. How much would adding in plumbing for a kitchen/bathroom into a basement unit and bathroom into the "garage BnB" cost?