What you can do is consult with a commercial real estate agent and see what the comps are for similar space so you can get a range of what to expect in terms of real estate value. See if that range matches what the seller is thinking. I don't see any benefit in paying for the appraisal now.
With respect to the practice, I do see the benefit in trying to establish the price now; however, just know that you can appraise the practice as of say 12/31/2011 in 2013 very easily.
1. Agree to the purchase price now
2. Agree to the closing date
3. Agree to when the parties need to back out before it becomes binding
4. Agree on stop gap measures to insure compliance after the back out date
5. Agree on the structure of the partnership
6. Agree on the building acquisition
All in the associate agreement without having to draft all of the other documents right now. That way if the deal doesn't go forward, you don't spend the extra money on the details contained in all of those other documents.
It seems to me your questions will be driven by how that meeting goes and the information that gets presented. I don't know what questions I'm going to ask of a seller\broker re: their valuation or asking price until I've seen what they've done, how they did it, the information they used generate their report.
Once you see this you'll be in a better position to know what questions to ask I would think.