Tell him Teins are better than Prodrive Stephen, he'll listen to you! LOL! When I did my car I started of with cosmetic stuff, like stickers, wheels and spoliers - silly I guess. But next came the handling mods which I'd recomend before any power upgrades. That way you can utilse the power that is already in the car, before looking for more. I started with Droplinks, then springs then the ALK. The springs were the greatest benefit, then the ALK; can't say I noticed too much difference with the droplinks, but I never really pushed the car with just these.
As Cal said (or copied and pasted ) the 2.5 do run a tigher bore, so be careful with the power, trust me, I know!
Good luck with it Mav!