If you go that route chances are good that you'll get a good car - doesn't mean it won't need some work and some money spent on it, but it won't be a rusty hulk like so many are from ol Blighty!
Here's a list of things you'll probably wind up doing at some point....
New suspension cones - they tend to flatten out over time and miles and make the car ride and drive like crap.
Brakes all around, shoes, pads, hoses wheel cylinders in the rear and so on, flush brake fluid
Suspension bushings and bearings, alignment
Tune up - valve adjustment, distributor, carb overhaul etc Replace the distributor with a new all electronic unit. Of course, if you get a fuel injected car you won't need to do anything but the valve adjustment, plugs and air filter.
Radiator replacement - only if it runs hot in summer weather, otherwise you're good. Drain and flush cooling system.
Oil and filter change....if you get an automatic be sure to get the right filter - it's different. Use high zinc oil, automatics use motorcycle oil, Jaso 10W40 MA2, regular stick shifts use 20W50 or 10W40 high zinc, not synthetic like Mobil 1
Exhaust system. An RC 40 gives a nice mellow sound if you want to do something other than stock. A good time to add a header too, and maybe get it ceramic coated.
Seats - front seat foams get old and collapse. New foams are available and any auto upholstery shop can change them
Tons of little projects you can do over time, none are real expensive and they all add to the driving experience. Do look for a local Mini club and join up - they are a ton of help and offer lots of fun things to do with your Mini. Once the pandemic is over there will be driving trips and meet ups you can go to that are fun.
Welcome to the Mini world, things will never be the same!

Edit: One other thing to know - Japanese cars were unique in many ways - most of them had a/c and were automatics, the engine came in two sizes - 998 and 1275 - I think you'll want the 1275. Most of them are fuel injected, and the dash is unique to the model because of the A/C. Some parts are being made now for these cars in Japan, and they are good, high quality parts - but a little spendy compared to the Brit stuff.