First of all...damn! Congrats on this opportunity.
I teach at FSI on one of the Lear models. The course is 3 weeks. I don’t know what the Falcon 900 duration is.
If you’re flying strictly 91, you attend a recurrent every year, and that’s 4 days. If you’re 135, you have training every 6 months Same 4 days.
The people who come through that fly for the rich, private owners, generally love it. They’re compensated well, have good schedules, you’re at your home base, you get all expenses paid....you could seriously turn this into a solid long term gig, as long as the family doesn’t decide to sell the planes at some point. You also get a couple nice type ratings out of it.
Be cool with them and get paid fairly, and be clear on the schedule requirements they have.
As far as the actual training...if you’re coming from the Cessna 172 world, the fast jets can be a system shock, but I’ve had people make it through with no issues, and I’ve had people struggle. If you’re just getting an SIC type rating, the checkride is much easier.
I will say that, as far as FSI is concerned, we REALLY want you to pass, you get consistent training, and we won’t send you to check unless we have high confidence you’re going to pass. We won’t send someone forward just to watch them fail.
Good luck!