Mateusz, time to grow the business! You have customers lining up to train with you (me included) but we are all going elsewhere because the 'front-end' of SmartAviation isn't working.
Take the 'hit' and hire some admin staff and buy some CRM software to track prospects. If you are unable to grow the business because of acft or instructors, then 1. invest, or 2. at least provide people with an answer (automated) saying you are full! That way we can all move on with our careers and stop wasting time chasing quotes or information on start dates.
Your training, location, prices etc. are all very attractive. You have a great business proposition. Now you need to grab the opportunity and spread the workload :-)!