Whatever you buy/look at lift it up on the blade (with the blade behind you) and make sure it can then lift itself up from the other end with the bucket. Ideally get someone else to do this whilst you watch the slew ring and king post for play (expect some play in the king post area at the hours you are considering, but use it as a guage as to how much wear there is in the machine). You don’t want any play in the slew ring (ie track frame wobbling about relative to the upper structure).
I’d be considering machines from 3.5 tonnes upwards if you are going to have to get someone to move them anyway - they tend to be cheaper ‘pound-for-pound’ as are a bit of an unusual size in the uk. Bigger machines often carry their weight better over soft ground as tend to have much more track on the ground - that’s something I’d suggest considering when comparing the models you have shortlisted (along with actual ground-clearance below the track frame, which becomes more relevant as the ground gets softer….).
From what you are saying whatever you buy/import should command a decent resale so it doesn’t sound like you can go too far wrong dipping your toe in.
Good luck - keep us updated with pics ideally!
(I want to come over fishing/drinking/digging once you are set up please!

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