You need to do a couple of batches in the LG incubator to get a feel for it, don't put expensive eggs in it the first go around. Once eggs hit the post office, the chances of them hatching decrease. Specially if you don't know your incubator well.
Going with averages, you might get 3 ducklings from every 10 eggs. Or, buy 10 ducklings from Holderread, and get 10 ducklings. You don't get money back on eggs that don't hatch. No refunds on hatching eggs unless they arrive broken.
There's always the chance nothing at all will hatch.
Personally, I would buy the ducklings from Holderread, grow them out, pick the best 6 for 2 trios, sell the other 4, use that money to buy an incubator, to hatch the eggs from the flock.