Dunatos if you want it to be on Lake Union. If not, CSR is now located near the Ballard Locks on the south side of the canal. Both can haul you for survey--change the zincs while its out of the water.
Are you using a buyers broker? If so, they will have the answers to all of your questions. Otherwise, the sellers broker should have suggestions on surveyors in the area. The surveyor can give you some suggestions on where to have it hauled.
If the boat you're buying has gas engines in it, buy a set of spark plugs for the engines. When you pull a plug for a compression test, replace it with a new plug that's been properly gapped.