Well... You could learn, and would, a lot by just doing it. But it would require a hell of lot of preplanning and studying before almost every flight, which it sounds like would have the time for.

You would absolutely be in over your head... But you might be able to swim up for air every now and then. It can get real tricky dealing with multiple FIRs at once when flying through eastern Europe and over the Mediterranean region, you've GOT to know how to read actual maps and use them. it can get stressful real fast.

As a "part 91" operator you'd have much less of a safety net as well. Then there is the dealing with local governments on arrival... which as PIC it sounds like you'd be responsible for. I don't know how that would even work (I've only done 121-supplemental).

Who would your FOs be?? Experienced? Wet behind the ears? If it didn't come with experienced/typed FOs I would walk away.

Overall, sounds fun and adventurous, but I think it would be a very brutal introduction into international flying.