Builder's Sales work is a different beast - the work itself (the transaction of the residential property) is easy but the front work is a bit more difficult and time consuming. It is unlikely a builder/developer will hire a lawyer (solo or small firm) just for the transaction of the completed properties. You get the client usually at the earlier stages sometimes even before the site plan is approved.
But yes, on closing date, typically we are just reviewing the Purchaser's executed docs, check funds, sign off the transfer (our practice is that the night before, we review all the transferee and sign for completeness, but the difficulty is that there is always going to be the Purchaser's Solicitor that leaves it to the last minute and needs to change something). Certain regions/cities/municipalities require consent on these transfers which make it worse.
Bad staff is a killer to any volume business - I have to emphasize the need to train staff well including associate lawyers. I have interviewed many great candidates but may not be the right fit for a volume solicitor's practice (a combination of good time management, organizational skill and keen ability to pay attention to the small details).
Residential Purchases is a land mine - I wouldn't recommend more than 10 deals a day for a single lawyer to handle. *EDIT my office staff (Real Estate Side): 4 full time clerks + 1 associate lawyer