Pulley 15% or 17% depending on what you going to use it for track or road ie wide open for a long time or quick blasts
Alta or kavs pulleys are the best and a good belt
I would not worry about the coil pack the standard one is good enough, but change your plugs to NGK BKR7EIX you must go up a heat range. When you fit your new plugs check tq them after a week or so then every few months minis do have a habit of blowing out plugs because they come loose
If you want a CIA go for the alta one or the m7 but what ever you buy you want it sealed from the engine bay as heat soak is your enemy.
As above orranje or Dave f air box or you can mod yours pretty simple and easy to do
There a few good threads here and on NAM
Intercooler the GRS (motor sport version) is very good the airtec is also very good to
Exhaust is down to what you can put up with noise wise I hate a dull brone on the motor ways, there are a few good sound clips on you tube. You could always do a one ball mod to you standard system.
Ecu remap is not really important at this time as the ECM is adaptive self learning but to a limit, but if you run into fuelling issues and need bigger injectors you will need a remap or tweak to yours
Any mod you do to your engine always reset the ECM this is done buy disconnecting the battery for 30 min (neg then poss to disconnect then poss then neg to reconnect) which you really should be doing when working on your engine anyway.
Have a look at you bypass valve to, as sometimes they fail or are not set correctly and you loose boost
I would get your car put on a dyno just to get a base setting check your power and most importantly your air fuel ratio.
Then mod it and do it again just to make shore your safe fueling wise and you should be running v power or similar after the mods
Hope this helps