My suggestions,
Spark plugs are are culprit for hard starting ! Clean, test and gap or replace.
Did sound to be cranking a little slow, I would fit a power socket so you can jump start with your car, most recreational aircraft use anderson plugs.
I would make sure choke are operating properly and pulling full on as it is an enriching system. Your engine sounds to be firing but not running as if no fuel to continue !
When a Rotax gets going it's a good idea to loose the choke quickly as not to foul plugs ! Do you do this ?