Sounds good, I'm happy to share all of the knowledge that makes a successful Iron Butt run, how to setup tools like Spotwalla and how to make sure you record everything right (fuel receipts etc) for verification etc.
250 km fuel range isn't really a problem, I did my first iron but on my old VTX which was pretty much around the same range, and 2-2.5 hours is a good "stop and get off the bike for a few minutes while you're fueling up" range anyways. Some guys with extended tanks go 5-6+ hours, but I can keep a fuel stop to under 2-3 minutes so I'm ok with stopping a little more often usually.
So long as that Vespa can maintain 120-ish (?) it's totally doable as long as fuel stops remain tight etc. I generally make one 20 minute stop at about 3/4 of the way through the run for a longer leg and back stretch, actual hot food, and keep the rest of the ride to rapid fuel stops and essential bathroom breaks - I pack food in my tank bag for nibbling along the way, and drinks. It's better to ride hard on an IBR ride at the beginning and relax if all is looking well around the 70-80% way (within reason), and finish comfortably a few hours earlier than the deadline at worst, vs the alternative - a lot of first timers make the mistake of stopping for too long or pacing too slow, or planning passes through major cities at the wrong time of day which can really wreck your required pace, and then the last 3-4 hours can be panicked (with pressure to ride faster) as the deadline looms and the mileage remaining is still high.
All in all it's a hell of an adventure! I love it.