Buying with a partner (or two) for beginners

[Allen Clark]

I am pretty new at this and have purchased two separate SFH in Seattle. One was ready to move tenants in and I've had that operational since January. The second one I've turned into a legal duplex and have the top rented out. I still have to finish the driveway and basement to complete the project. I told myself I would not buy another property until the work was all done on the previous house.

However, an opportunity has come up but I would need a partner or two to get this done comfortably. 

A colleague of mine invests as well and I respect her REI work. We would work fine together. How does one structure a deal such as this typically? Houses sell fast in Seattle so we need to get an all cash offer in quickly. Is the general advice to go to a real estate lawyer pronto to draw up a partnership agreement? What have people done when doing this with one or two partners?