So for the first time ever I failed the GTT and now the birth centre has dropped me and I'm well aware of most hospitals stance on GD and how they manage it. So I'm freaking out big time.
That totally sucks. Although you have GD, you don't birth any differently. OK, it may (but unlikely) require some additional care post-birth for bub but it does not, one iota affect the way you birth. So don't let them pull that one on you. I had diet-controlled GD with DS1.

Baby is not measuring big, if anything he actually measures behind! I lost 7kgs in the first 25wks because of HG and have only put back on 2kg at this point in time so I am well below starting weight. I've been watching what I eat because of the HG so I'm not eating anywhere near as much sugar etc that I did with the other three kids.
DS1 didn't measure big either. When I was first diagnosed with GD, my Ob made noises about induction at around 38-39 weeks as GD babies can be bigger. However by the middle of my third trimester it was obvious DS1 wasn't big ... then she made noises about my placenta possibly not functioning as well as it should ... and possible induction. Sigh. And don't think it's what you're eating - you didn't cause your GD. It's purely the make-up of the placenta. I didn't get GD with my younger two boys and I did/ate/weighed pretty much exactly the same.

My biggest concern is what happens after birth, I am not interested in having bub be separated from me to go for monitoring in SCN. I am not interested in formula feeding. I don't even want to stay in hospital postpartum but I will compromise on 24hrs post birth.
Didn't happen with me. DS1 weighed 2.9kg at birth (born spontaneously 39w3d) - the paed didn't even check out his blood sugar levels afterwards. Ha, DS3 was born at 42w at 4.5kg and the intern (not a paed) insisted on checking his sugar level when I was 5 mins from discharge (4.5kg is borderline for when they automatically check blood sugars). The fact he was 2 weeks overdue didn't appear to sink in. Of course his blood sugar level was fine.

How many people have avoided induction, after birth monitoring and formula top ups?
With my GD bub, no induction, no after birth monitoring and no formula top up. As he was smallish he tired easily so BFing wasn't a piece of cake initially so he had EBM top-ups and was happily BFing exclusively within 10 weeks or so.

I guess GD can affect people differently. I had to do the blood (finger poke test) four times a day, and my levels were a bit over the shop at times, but generally within acceptable levels. I had to watch my diet, but really it wasn't that hard. Obs and the medical profession - to me - overuse GD as a way of controlling your birth. So my advice would be to stand firm. For instance, my waters broke spontaneously with DS1, so I went to hospital for monitoring. All was good, I was 1cm dilated, so I said "I'm going home to establish labour". The midwife was happy with that, till she spoke to the Ob (not ours, but her partner who was on duty that night - private hosp). The Ob wanted me to stay and be monitored because (1) my waters had broken, (2) I was having mild contractions and (3) I had GB. My response. Yep, I've got very, very mild contractions, I'll be back in the morning if nothing much happens and how the heck does GB affect my labour??? See ya. And I went home, only to return less than 3 hours later at 7cm dilated and got a natural VB birth. Bub was born about two hours after I went back to hospital.