I disagree slightly with making one broker “accountable” for everything until closing. The lender, lawyer, appraiser and any condo-related contacts control parts of the process. A broker cannot guarantee their response times.
What the broker can own is the communication trail: dated requests...
The Toronto local board looks like the obvious starting point, although I am hesitant to build a duplex model from price records before I understand the property differences behind them. I am a real estate agent, but I am currently here to learn more about duplexes, transaction costs, renovation...