Re: #1–how? could you make a lace edge (instead of ribbing at the hem–Yes
could you make a lace swatch and use it a pocket? maybe
could you make a lace swatch and inset it in center front like a medalion? again, maybe!
Re#2–some lace is done with lace weight yarn, some is done with cobweb weight yarn… (even finer than laceweight)
most lace is knit on slightly larger needles than you’d expect–lace wieght is frequently knit on 3.5mm to 4.5mm needles and blocked heavily to stretch out the lace
cobweb weight yarn is often knit with 3mm to 4mm needles
and it too is blocked to better show off the lace.
i can’t imagine knitting with darning needles they are too short hold, (the fineness isn’t a problem…
some needles are super fine (2mm, 1.5 mm, 1mm!) (in US terms these are 0, 00, 0000!) but i don’t usually use these for lace!
can you sew store bought (or even real lace (ie bobbin lace) onto knitting–sure! but a jumper (that is in US a pullover sweater!) is pretty casual wear… and fine lace with casual (sports clothes) can work but fine lace with a pull over?
a cardigan/knit jacket would look better in MHO!