Well, if it's any help, Mach 44, In the days of yore, all I needed to start my FIC course was a PPL, IMC and 150 hours in command! For all sorts of reasons I wanted to instruct and the main reason I wanted to do it was not that I eventually wanted an airline position, but that I had been taught to fly for virtually nothing by a small enthusiastic flying group. I wanted to put something back to return the favour, so I did for the next 25 years! It was a great hobby, I made a lot of friends and the fact that the pay was virtually negligible didn't worry me as I was teaching enthusiastic people to fly. Eventually I did get my professional licences and did end up in the airlines, but that was not my original intention and I didn't even think about my CPL writtens until I had over 1000 hours.
In the end I gave up because I got a bit fed up of teaching a load of people to fly merely because thay thought that they could make a shed load of money at it, and daddy was happy to subsidise them. As, by that time I had gone through the pain of acquiring my ATPL and was by this time in the LHS, I got a bit fed up of teaching these individuals to fly. "I would like my cut" I used to think and eventually lost enthusiasm.
Of course these days, things are different and a CPL is needed before you can get a FI rating, however my example should indicate that an enthusiastic person with a good standard of PPL knowledge can most certainly qualify as an instructor and be successful.
P.P.