I use braid mainline for 95% of my fishing and since a breakage in the early days, an Ouse Barbel, probably a double, I always use a swivel to connect the braid to the invariably mono/ fluro hooklength. Anything from 15lb fluro for Salmon down to 0.11mm nylon for Roach and Dace.
Braid is fantastic stuff and really allows one to bully fish out of snags and otherwise control the fight. The longer the hooklink the more stretch you have is something to bear in mind, I find about 2 feet is long enough but always keep a good bend in the rod.
To give an idea how much pressure you can put on, use your usual rod and reel set up, attatch the line to a 2lb bag of sugar, a 2 lb sea weight or similar and lift it off the ground, you'll be surprised, I guarantee it.
For your margin Carp fishing I'd be using an 8lb nylon hooklink, Drennan series 7 or similar 'normal' nylon. Heavier if necessary.
I'd avoid the Berkely braids especially Fireline, it fluffs up and frays terribly. My favourites are Spiderwire, great on a fixed spool, Rovex Viros NXT is also good. Spiderwire is very thin for its B.S. and you'd need well over 30lb to get a practical diameter.
My favourite for the centerpin, mainly trotting is definitely Fox Jigsilk in 0.13mm, can't remember the B.S. but it's well over 20lb (22.5lb I checked), no fraying, ultra smooth and bright yellow, great for mending the line as it's so visible. It's a flat braid, which explains the seemingly small diameter, so doesn't suffer from bedding in very much even with the whole 130 metres on. It's sold as a sinking spodding line, don't believe a word of it, all braids float like a cork.
Knot wise I use a palomar knot to the swivel. I was told by Don Neish, famous tournament caster and tackle dealer, who'd done research on braid knots, that this gives about 70% knot strength. The same research showed that the grinner knot only gave about 50% knot strength though.
Obviously use whatever knot you favour for the nylon to swivel knot. Small swivel for fine nylon, slightly larger for heavier.
Best of luck with it, it brings a new dimension to your fishing, even Roach and Dace feel a lot livelier and bigger on the braid. It brings a whole new dimension to touch ledgering too. I can feel Barbel in the swim long before any bite indication!