You can't use epoxy over sealer, so it's an either-or proposition.
You can get floor "epoxy" at home depot, or lowes, but the general opinion around here is the single-part, consumer-grade epoxys aren't very durable. A good epoxy is somewhat more expensive, but the price range is from slightly-more expensive, to WAY-more expensive.
There's about a million threads on the epoxy subject around here, as to which ones people have used with good luck, and not-so-good luck.
Just one thing, above all else. Proper preparation is absolutely critical, even on new concrete!