Once you start getting mod-specific maps (not just generic ones) then you're looking at spending ££££ and there's too many combinations of mods and maps to advise on any specific one. Exhaust (I think the 8L downpipe is the restricting section), front-mounted inter cooler (to stop intake temp limiting boost), d/v (better engine response on and off the throttle, might speed up spooling too), turbo charge-pipe (never remember what it does exactly) etc all add up for maps beyond Stage 1, but you'd be better planning the mods then getting a suitable map than getting the map and then buying mods to match it.
If you get a stage 1, things like an exhaust and intake will likely still add slight gains to the power (the ecu should be smart enough to optimise itself for the inc flow etc). Don't quote me on that, could be a slight misunderstanding on my part.
Like I said though, head to the 8L section and find out what output other people are running, and what combo of map and mods they use to get there. If you've got a plan in mind (300bhp+, big turbo conversion, value for money etc) then use that as a starting point. After a generic map, power starts to get more and more expensive in term of bhp increase per £ spent.
