Getting nr 200bhp out of the RST is pretty easy. So long as the car is mechanically sound, most of the 'bolt on' bits will do the job. Exhaust, chip, cam & decent panel filter in the stock airbox. Unless the box has been refurbed is will go with the increase in power so get a spare, or keep some cash aside to get it done.

Taking it upto and over 250bhp takes a considerable chunk of wedge. IMO for a reliable 250, you would need to uprate box, pistons, rods, bearings + run on proper management