You want a decent electronic boost controller. 0.5 spring is fine mate run that to a bar no problem uprating the spring won't make a difference..running a decent ebc will!
There is a Jam ecu on ebay at the minute I'd make a start with that, then a decat and exhaust there is no point in upping the boost without a 255 fuel pump or manifold due to restriction flow of the stock one. Think about coilovers to imo.