Well it's been about 3 years since I imported my car so costs/exchange rates will have been vastly different than todays market.
But I was in the same position as yourself, never having done it before and finding it hard to get any concrete information. In the end I used Torque GT to import me my DC2 into the country, as have many people on here. They are regarded as one of (if not the) best import companies in the country. They will source and import a specific car for you so theres no competition with any other buyers in the UK once the action has been won in Japan. I would 100% use them again.
As for fresh import vs a car already imported. It all comes down to your preferences for the car and budget. If you don't mind something that might need a bit of work and be a little bit cheaper on the wallet, then a UK sourced car would be your best bet. Thats not to say that all of the cars already in the UK are of lesser standards than one straight from Japan, as many owners over here will have no expense spared on looking after their car!!
I got bored of looking for the right car in the UK that met my requirements so went for a fresh import as there are 10 fold more cars to choose from on the Japanese market (obviously). But with that you have to pay a premium price. Which is understandable with shipping, import taxes etc.
If you want any more info or a run down on the prices etc drop me a PM, I'm more than happy to help