Starting note.... Spitfire MK IV is a 1300, Spitfire 1500 is effectively the MK V (but that's just model pedantry, no really relevant)
I came over from the land rover world about 10 years ago when I bought a Spitfire 1500 - my first classic car (land rovers aren't classic cars, they are just old/older land rovers 😉 ) my advice would depend on how handy with the spanners you are etc. Most mechanical stuff is DIY sortable, but I (personally) hate having to sort bodywork out, so I'd go to town with any you look at hunting for rust (usual places, chassis, wings etc.), spend the extra for one with overdrive if you plan on doing any long trips or higher speed roads/motorways. If you are going to thrash the car (driving up alpine passes for example) one with an oil cooler is a good plan if it's a 1500 (1300 not so bad) but these are relatively cheap to buy/fit - so not a massive deal. SEATS are expensive (relatively speaking) to re-trim and re-foam, so a car with decent seats fitted is a bonus.
See if you can find an active local group for the club and go along and make new friends - you might find somebody with a Spitfire happy to help you look at possible purchases, or their cars might give you an idea of what to expect?