Investment Sales: How to pick an area to start out in, NYC. Explain process from start to finish (canvass, call, meet)

Interested in investment sales in NYC. Trying to figure out the process, how does one pick an area. For NYC let's say you want to do multifamily investment sales how do you decide? Do you look at the Bronx because multifamily there is less expensive than other areas and you may be able to sell more for smaller amounts. Or do you go with Manhattan, look at areas such as Harlem for multifamily? Can IS brokers discuss how they picked an area, how canvassing works, and how they find so many owners to call (i.e. 300-400 call a week expected). I've read threads that explain parts, but can anyone give a detailed response for this process.