EU standard is minimum 600kg (1325 lb approx). You can attach the webbing with a single line passing through each eye and the jackline. This will need only two knots. Use any knot you like.
Assume you are falling some distance. Assume the line is tight, and there is a "tight-rope effect" force multiplier in action. I bet I can grab your 1300# line and snap it with a pair of gloves in the middle. Certainly I can after knots, chafe, and sunlight take their tolls. I wonder if the 1300# is the Safe Working Load (SWL). With a common 4-5 safety factor, that's close.
All gear for falls - mountaineering, sailing, or OSHA - has requirements around 5000-6000# because the math works out about the same. All of the gear is built to that standard.
Knots are fine - just make sure that they are high efficiency knots like a figure eight on a bight or other. The attachment points need to be very solid - probably not handrails or stanchions.
Some like tubular webbing, because it isn't too bad to walk on, but the nylon stuff doesn't handle sun well - within 1 year it will be ~50%. I use 1/2" line, because I run my jack lines above the deck and it handles sun well, but multihulls are different, and that is probably not for you.
Perhaps the main thing is to keep your lanyard short enough to keep you on the boat. Hanging off the side is a real problem.