I consider myself a B- when it comes to splicing. Better with 3 strand, lots of back splices and loops but no anchor splices. Plaited line is a little trickier. Done some loops and one anchor splice which worked so, I guess, OK.
First, and I think you know this already, no loose ends. Stating the obvious.....
Second, there looks to be a hole there. Mis-tuck???
Third, that doesn't look like nylon. Lewmar specifies it. Is it Cotton?
I see your inner "Yankee Frugality" is showing but 3 strand nylon is CHEAP! Why not save yourself and buy what you want. No splices, no headaches.
A splice to be used in a windlass needs to be flexible. Too big and tight, it won't fit. Too loose and it will snag and fray. One trick is to splice it snug a few tucks then roll it in your palms to loosen/even it out. Tapering plait is easy. You are working with 4 pairs so you just cut, burn and drop one from each pair for a few tucks. I've never had to taper 3 strand, I guess you could halve each strand then cut, burn and drop for a few tucks.