Hello and welcome! Insurance wise just go on gocompare or similar website and get a quote, that will give you a rough idea, too many variables for us to consider! Running cost wise I find the ek9 perfect - never had a supra but I can imagine it being more expensive. EK9 really does not differ from lets say EK4 very much in terms of running costs, same road tax etc... Most common problem (and arguably most serious) will be rust, check rear arches, underside, engine bay, basically whole car. Gearboxes tend to have issues with syncros so make sure there are no crunches. And also ask about oil consumption, there will be cars that use no oil at all - perfect, low oil consumption is however fairly common and I wouldn't panic because of it. Excessive oil consumption is bad as with any other car. That's about it, rear wheel bearings seem to be prone to failure and are £130 each plus fitting, something to check as well!
And finally, expect to pay £4500 - £5000 for a nice clean standard car.