Having read thru this thread I would tend to agree with the main upgrade being a remap.
I fitted a green panel filter 5 years ago and clean it regularly (as per instructions) and have had no problems.
I had a custom remap shortly afterwards and it read: before 157bhp, after 193bhp/292lbft.
I have just recently got a cat-back non resonated Milteck exhaust fitted but only 'cause my original exhaust t finally gave up the ghost after 7 years!!!!!!!!
Anyway, enjoy your mods
Oh and last month I fitted the allard egr delete pipe, to keep my engine clean but had the dreaded elm light come on - hay ho