Sadly Connor, your logic may not be quite as sound as you think...
Once you have saved up and got your 2.8 you will look at it and think.... "new exhaust, new suspension, air filter and other bits and pieces..."
Yes but then at the end you look at your 1.9 and think I've spent so much I could have bought and 2.8 and added on slowly to that...!!
I look at my 2.8 and think it's had more spent on it than what would have cost to buy an M...it never ends!
However that is over a period of time and a lot of it was refreshing old parts which I would have done to a similar mileage M anyway.
And to further console myself I tell myself an M is just too much power anyway...and I make sure I never drive one so I am non the wiser!!
Or look for one that already has some of the bits that you want done, typically modified cars sell for less than original (which is funny because original cars now wallow like boats compared to one with fresh set of coil overs etc!).
My view is to Get a 6cyl and if you short on funds after purchase just modify the exhaust and air intake (there are cheap/free ways) and liberate the sound then the rest doesn't matter much after that! The big fun for me is the sound with roof down, just great.
Then save up and add the mods you want over time.
But get a 6cyl!