I think you can skip the 'massive pram' stage. I got into slings properly when DS was a few months old and then used a sling a lot until he was about 1.5, hardly ever used a pram until then but then began to use a buggy more as he was very big and a late walker. We still sling him occasionally at 2.3 though! I made a load of mei ties and definitely found these the best for back carries etc - tying 'tibetan' gives you a lot of support.
I ended up buying a cheapo 2nd hand mountain buggy as we live in the country and it has a very tall handle (we are both giants) but if you got on well with slinging and lived in London then a lightweight umbrella-fold buggy with a shoulder strap would be the obvious choice.
You definitely need something for grandparents / childminders though. I got an ancient buggy off freecycle for my parents to use and we had a Quinny buzz that we hardly used at all once we had started slinging but which my mil LOVED as she liked having a 'proper' pram to wheel around her village. I'm fairly sure if we hadn't given her that to use she would have bought her own pram for her house! My mum did use a sling a couple of times to settle DS but would not have felt confident or able to take him out for the day in it so that is definitely something to bear in mind. There are so many good cheap prams available on eBay though, you definitely don't need to spend a lot on one!
No.2 now on the way and I have bought a big all-terrain double in case it is v icy (only time i really hate slinging) first couple months (due in the winter) but this time round I will be slinging from new-born a lot more. I found once I had ditched the pram and got confident with front & back carries DS was just so much happier in the sling, slept better, interacted more, became a calmer little guy in general. I loved not having to worry about steps, lifts, doorways, getting on and off buses etc. Also found once you don't have a pram to hang all your crap off you realise you don't actually NEED that much stuff which is quite liberating!
You do need to tailor your wardrobe slightly, the dreaded waterfall cardi is great as can wrap extra fabric around baby in sling to tuck in toes etc.
Slingmeet is a great idea if you can find one, worth checking out 'real nappy' meets or asking the NCT in your area as there is often an overlap between slings / cloth nappies and other faintly patchouli-scented baby activities 