I think this is a really difficult question to answer to some extent - it is one of those how long is a piece of string type questions, but let me give you some ideas.
Firstly, your client base will depend on the price point you set and the services you offer, in addition to the times that you work and these factors will determine the best place to work in London for you and your needs.
Working in busy areas like Old Street, Liverpool Street, Holborn, Euston and areas like that may attract lunchtime footfall from office workers ( whomever may be left nowadays post Covid WFH era).
Areas around commuter train stations have always been good in the past pre- pandemic times as many men would find getting a service before they headed home to the leafy home counties really convenient. So areas like Waterloo, Charing Cross, Euston, London Bridge, Victoria, Paddington, Liverpool Street, St. Pancras and King's Cross were good for getting those commuter clients.
Obviously a luxury apartment base in Zone 1,2 or 3 is going to be pricey so once again it depends on distance from Tube stop, if you have parking or is it on a bus route and easy to get to for a client to find you without any hassle or issues. Some girls swear by Victoria, Sloane Square, Knightsbridge and Kensington but while these areas work out to be a gold mine for some, others find the client base dry and dusty.
Bayswater, Paddington, Shepherds Bush and Hammersmith work out well for others, as these areas are very well connected transit wise and fairly Central.
If you are thinking of venturing to the outskirts, what I call car territory, you may pick up a client base from men who are using their cars to and from work and should consider flats that are not too far from motorways or exits but also not smack dab in the middle of a traffic route from hell. Areas like Greenwich or Lewisham in the SE area or Golders Green/ Edgware in the NW area for example.
Some working girls love the Heathrow area for the incoming / outgoing travellers, while others hate it.
Before settling on an area, it might be best if you tour London and work from the different areas until you find a good fit for you and your working profile/method/criteria.