Just a few things to think about.
I have a 1995 UK GT4.
Any GT4 you get will most likely have issues and spares can be a real problem depending the year you get.
THIS WILL BE A PROJECT CAR.
Saying this I would not change my UK spec GT4 for the world. I used mine daily until the MOT was due and will be using again daily as my main car once I sort out the ABS sensor.
I previously owned a 1998 Celica GT SSIII (ST202 with a 3S-GE Engine). It had an issue with the front I never solved it kept destroying wheel bearings. In the 3 years I owned it I had to change both front ones twice each. I also changed the 2 front drop-links (known issue on both the ST202 and ST205) hoping this would solve the problem (nope). Other than that regular oil changes/filter and the normal new battery, tyres, pads, fluids and disks all round(I do this for all the cars I buy).
My GT4 is a different kettle of fish. So far I had to or need to
New battery (The old one is still in great condition and now a spare/camping battery)
replace both fuel tank straps (£38.22 each + Delivery). One done and one to do. One side needs a new bracket ($26 + Shipping from Japan).
Rear brakes Pads (all for pins needed drilling out). Eventually found reconditioned rear calipers about £160 each but I had drilled out pins by then with a £80 pillar drill)
Front left ABS sensor (in process of getting a replacement now. $300, note i could only get the right hand one so i have to cut the sensor off and reconnect it to the original wiring)
Some welding underneath just near the fuel tank. (Non structural and not exterior) Chassis is sound but does need urgent cleaning and resealing.
Fitted an 2din Android DVD player in the dash which did involve an hours work with a dremel and a small file to make it fit.
Get as new a model as you can. Particularly one built after July 1995 as they changed the abs systems and finding early abs sensors is next to impossible.
If possible get a 1998/9 model as they will also be OBD2 (not sure when it became standard but my April 1995 GT4 is only OBD).
You say insurance costs would not be an issue for you but getting insurance on an import is huge postcode lottery. I phoned several import specialists and main stream insurance companies as well as price comparison sites and the difference could be upward of £500 more for an import than for a UK stock car. My advice is check with price comparison sites and if the number plate comes up as a GT4 insurance will be easier. If it comes up unknown or a different car such as Celica GT or MR2 then you WILL have phone and trust me you will have issues. I put a caveat here. Where I live it was a much larger difference in price than it was in a slightly smaller town only 25 miles away.