161bhp is a bit specific isn't it

The first thing to point out is stop thrashing your 6th gear about, it's made of a synthetic material and cannot stand the torque, it will end up shattering and taking the rest of the gearbox with it, if you google 'm32 gearbox' you'll see all the problems people have with it and unfortunately it's used in the mjet

Only ever use 6th for cruising and do regular gearbox oil changes
Personally, Id do a few mods to the car before a map to get the best power out of it since that's what it seems you want.
It's a 07 reg so you're lucky, unless the original owner was mad and payed £700 extra for a DPF then you don't have one, you have 2 cats instead, if get them both taken out, the one after the turbo can be replaced with an astra cdti decat downpipe from ebay and the 2nd one just be replaced with a straight piece of pipe at an exhaust place.
Fit a blanking plate to your egr at the inlet manifold side, it will put a check engine light up but when you get your remap the mapper can remove that and also close the egr valve permanently, might be worth getting the inlet manifold professionally cleaned, give terraclean an email most of their providers can do that for you.
Then there's other stuff, like a forge intercooler. An induction kit will add a nice woooshhh sound especially when you press the clutch in but uses a lot of fuel. After that the only thing to do really is a hybrid turbo which is expensive.
Then you get a remap and you should see a good safe 175bhp but the main thing is you'll have a lot more torque which is most important.
No matter what though, with a remap you need to take care of the car, regular 5k servicing with good oil (while im writing my life story i'll recommend fuchs titan race pro 5w40, and for gearbox oil fuchs sinto fluid 75w80, the best 2 oils for this car imo)
ALways let it warm up and cool down too since the turbo will be under a lot more stress that's very important, after a ragging about, leave it idle for 30 secs or so ect....
hope I answered every question haha would of been nice for someone to do this for me when i started off, no matter what even with just a remap these things absolutely fly and tuned properly they will eat abarths for breakfast
-kyle