Congrats James!

I see on the forums so often people panicking as soon as their wife develops a baby bump thinking they need a bus all of a sudden. Maybe it's a male nesting thing thinking they have to be sensible and grown up?
My eldest is now 18 years and we managed perfectly ok with my Polo G40 when he was a baby!
Face it, we go out and be all responsible and buy a huge expensive pram that costs hundreds maybe (mine didn't!!!) then decide we need to spend thousands more on a new car to fit it in. It should be the other way round - you have a £35k car so find a pram to fit! After a very short time pissing about with a huge buggy most parent resort to a cheapo fold up thing anyway that's light and nimble so can be carried up steps or onto busses and will fit anywhere - not least of all when you get fed up with your hallway being taken up by a massive pram!
The Golf is a big car and plenty big enough for lanky teenage kids never mind a two foot long baby.
Yes the boot on all mk7's is much smaller than a mk5/6 (I don't give a toss what VW say, I know for a fact as I've just come back off holiday last week) but it is still big enough for a pram.
As for the three door vs. five - it doesn't really matter. I did find when mine first started in front facing seats in the back that it was easier with a three door mk4 Golf GTI as the seat slid forward properly on the tilt and you could sit on the back of the front seat and lift the baby into the seat without too much bending or risk of hitting either your or the little'un's head as you got in.
A Golf R is an amazing bit of kit so why not just find a pram that fits the car not the other way round.
I wonder how those guys who are leasing one for 50pence a month would get on if they suddenly decided their circumstances changed mid-term? Off topic I know.
Oh, and as for trips, if space is that bad then it costs about £80 to hire a decent sized car for a weekend and you don't have to worry about the thing getting all muddy.