congrats on the purchase and welcome.
the 600 twins were great sleds. the 98's may or may not have the corrected rings. how many miles does your sled have now?
two known weak points were the ring issue and the primary clutch. not that the clutch had any issues, but lack of routine maintenance shortened the life of the wear components. for some reason the twins liked to quickly wear out the bushings in both the rollers and the weights.
as for the flashing light, that is a self diagnosis function. the three flash is normal, and in addition, if other conditions arise pertaining to this function, other flash codes will display pinpointing problems.
if your in the states, your fuel capacity is almost 12 gals or 45 liters. some other info that may be interesting or not:
dry weight: 509 lbs
overall length: 108.7"
front travel: 9"
rear travel: 11.5"
mileage would depend on snow conditions and riding style. my 97 saw a few trips over 100 miles with fuel to spare with the wife riding it. if your sled is stock, no aftermarket pipe or can, regular unleaded fuel is fine, if its good.