Your situation sounds familiar! I have re-chassis'd 3 S3 LRs and had a 2000 Disco 2 so was expecting RUST. Not so!!
I have done about 4k pa since ownership in 2018. I got a 4lt 2000 with 109k on for relative peanuts.
I still have no headlining but the PO had stripped out the fabric really well so who needs to look up!
Speaking personally, if you are only doing 3-4k pa, is MGP really that much of an issue? I know many on here will sing the praises (justifiably) of a well designed and set-up multipoint LPG system, but to my mind, at these annual mileages, it just adds complexity and additional servicing costs.
Add in that LPG service stations are becoming rarer by all accounts then it isn't necessarily going to help, depending on where you are in relation to a sales point.
Double + for the advice on the EAS - I drove a vehicle before buying (along with 8 others) that was on springs and was massively underwhelmed.
I would also recommend looking for a Thor engine'd (late 99 onwards) vehicle which generally appear to suffer less problems - but that can very much depend on PO maintenance.
I spent the first month, before using in anger, replacing rad, water pump, viscous fan, hoses, coolant, air filter, pollen filters, spark plugs, engine and gearbox oil and filters and overhauling the EAS Compressor - all of which has repaid me handsomely with no problems on the road. I have also replaced both front shocks and had a front wheel hub/bearing replaced, and swapped out a stiff gear lever mechanism and done the infamous heater matrix O rings.
Most jobs were a breeze but the O rings were less fun, I'd have to admit! Good luck and keep us posted!
All in all, in spite of my initial worries (given the reputation), I have really enjoyed the experience and I love driving her. I am approaching a service, after 5k miles and will redo oils and filters and may have a look at the ARB bushes and steering damper.