splice is a way of joining two ends of nylon so theres no knot, have to admit, my first longnet, I just undid the knots,slipped the end pins on and re knotted it, and it worked ok for me
you wont need to make the top and bottom longer, as you want it bagged, not stretched out, look at your mum's net curtains, they should be twice the width of the window, gives them a ripple effect, well the same goes for your longnet, so whatever length it is, deciede at what distance your poles are going to be spaced at, and tes, you'll either need grommets on those poles, or as suggested, wrap a bit of t