If two people are bringing in work, I would forgo finders fees for the first year. I'd split the profit 50/50 and consider the sales work a necessary evil to get the opportunity to perform some work. After a year, you'll have a feel for what an appropriate revenue sharing agreement might be.
Should you get repeat business, it gets messy on who would get the finders fee for the 2nd, 3rd, 4th time they hire you. Does the person who initially brought them in get 10% for every repeat client or is it a one time only deal?
I've heard that businesses usually lose money the first year, so I wouldn't be paying any partner 10% off the top until the firm made some money!
The arrangement you are describing above sounds ethical, but I'll also mention that giving kickbacks to outside people (architects, building inspectors, etc) may or may not be ethical depending on who is paying the job and the disclosure you provide. But your arrangement seems ok.