Nice notion, but not worth it
As a person with a lot of sporting gear over the years, my experience with renting or lending out has not generally been positive. Stuff gets broken, lost, torn, dented - plenty of "ooops factor". I really want to be nice to folks entering a new sport, but i have been burned too many times in the past. Right now I maintain a "second line" of camping gear to lend out to folks - or I should say I did do that until someone "lost" the tent.
And I wouldn't lend/rent out a surfboard unless it was a a good friend and the board was a surftech...
It is a good hearted idea, but won't fly for me.
My two cents