Be careful.....once you buy a monster you may never buy another bike ever again !!
That's been my experience with my 750 anyway (7yrs and counting).
The old style monsters, especially the 2-valvers, are particularly nice to work on, with everything being easily accessible. I have no personal experience of the newer style monsters, but I believe they are a bit more fiddly.
Carby models suffer badly from carb icing in the winter (possibly of interest in your northern climate), but a dose of pro.fst in the fuel sorts things out. Injected models avoid this, but the downside is the potential high cost of replacement electronic components if anything goes wrong.
Many used bikes will have had a tail chop, which looks nice and clean but isn't recommended if you ride much on wet roads.
Charging circuits seem to be an Achilles heel, with many reports of reg/rec failure. The general view being that the alternator wiring and connectors are borderline in design. Telltale acid staining is common on the left hand frame rails.
On my bike at least, the front suspension is a little hard on rough roads, but its fine on normal surfaces and kinda suits the character of the bike.
Plastic tanks fitted to some models can swell and distort if using high ethanol content fuel. Steel tanks often suffer leaks around the rear hinge bracket, possibly due to lifting them carelessly when they have a lot of fuel in them.