Being good at their craft does not mean that they are good business people or partners. Your business is embryonic and a bad partnership can kill it, and your reputation, quickly.
My first thought is, before committing to something binding like a partnership, just formalize the referral relationship for awhile and see how it works out. Carefully observe how they manage their business. See what their customers confide about them to you.
Then, if you decide to go forward with a formal partnership, a certain amount of due diligence must be done, to include examining each other's books, business performance, credit, etc and a partnership and operating agreement must be created. This process should not be rushed into.
The stakes are high for your business, be patient in pursuing shortcuts to growth. You are on a good trajectory and are on plan. Be cautious in going off path because it could be irreversible. I hate to be pessimistic, but the wrong partner could easily make your dream a nightmare.