Buy a Decat for the exhaust, then from the decat back have a stainless steel exhaust.
Get a BMC panel filter.
Boost the turbo pressure up a bit.
Get a remap after you do all the mods.
You can put in SDi injectors instead of the standard ones.
Cost:- Decat pipe off ebay about ?25, s/s Powerflow exhaust ?250, remap about ?200. SDi off ebay ?10 to ?100 but I've not bought any.
Dont think just chaning the MAF will increase bhp, but will make it run properly, get the right miles per gall. or kilometers per litre. And will rev better.
Think you might have to have a trip over here to get sorted.
My one is 134 bhp, 150 bhp can be found with the SDi injectors, best of luck and hope you can find a garage in France who can tune your one.