About the same cost to get 250kw as 290 300ish just more lag and different parts eg different turbo, better clutch etc. So you need to decide on your own how much power your going to want and upgrade the usual bits to handle it. Plenty of results/ dyno graphs it the turbo upgrade thread.
Plenty of people asking "what do I need for 250, 280, 300kw etc" and plenty of answers to these questions...
Find these threads and start with the supporting mods first otherwise you will have to pay for twice as many tunes.