I have a small fleet of decent rental mountain bikes in Prince Albert all bought used on Bikehub . Granted that you will have more tourists in Knysna than what we have , do not expect to make money on rentals . If your guest house pal wants to do it as a service to his customers so be it . Few people that rent bicycles look after them properly and you better not be finnicky about scratched frames . As to the sizes go for 2 x S 2x M and 2 x L .