Rathikrishner = a miss-spelling of "rathikrishna", a young lady from India who has a reputation for producing excellent models and controllers from pretty much zero resources, apart from talent, imagination and enthusiasm.
quid = slang for "pound".
Having a prop shaft of 1/2" does not demand a 1/2" motor shaft. A multi-part coupler can have different sized ends, as can a one-piece coupler. If pulleys are used, the main requirement is that both use the same size/type belt.
Since a square rigger does not need to go like a racing cat, a quite modest motor, geared down to match the prop, will do the job. If looking at auto scrap yards as a source, motors from radiator fans and heater fans and window winder motors geared down are good candidates, as are the battery tools mentioned.