Hi Stephen, if the numbers work, you could always rent it for 1 year and then sell if it's not working for you. If you haven't already done so, I'd work and re-work the numbers in a spreadsheet to ensure that you've got the return calculated as accurately as possible. Numbers to consider:
I appreciate that the tenant may pay the first three of these, but still mentioning them in case not.
Utilities Water
Utilities Electricity
Utilities Heat
Utilities Garbage & Recycling
Snow Removal (does it snow in Seattle??)
Landscaping
Proeprty Taxes
Insurance
Mortgage Payment
Vacancy - 7 to 10% is national average
Property Management - Roughly 10% of total rent (Call a few local property management companies to get actual quotes if you haven't done so)
Repairs - Oven not working, plumbing etc.
Capital Expenditures Reserves - What shape is your roof in? etc.
Also for your return, you'll want to calculate that based on the money that you've personally invested out of pocket into the place. If I'm understanding your post correctly you might be calculating the return based on the market value of the property, i.e. 775k - but it doesn't sound as if you've placed 775k of your own money into the property, since you've stated that you have a mortgage.
What you'd want to do instead to calculate the return is you'd take your annual rental income, minus all of the expenses in a year, expenses being everything that you're paying out of pocket in relation to the property, such as the examples above, and that gets you your cash flow. For example's sake, let's say rental income's 36k a year and all your expenses are 34k a year. Your cash flow is 2k a year (36k - 34k). If you've placed 150k into the property, i.e. down payment etc - to calculate your return you'd calculate:
2,000 = x% of 150,000
OR
2,000 divided by 150,000
which equals a return of 1.33%
The wild card here is, Seattle as I understand it has had a strong housing market in recent times. A decade from now could you have an additional $300,000 in equity? Potential appreciation is something else to consider in addition to your annual return.
Good luck!