I am mad about Minwax wipe-on poly.
You shake it up, pour it onto a soft rag (I use the t-shirt rags you can buy for $2 a pound at Lowe's), and wipe it on. I have a pair of rubber gloves I use for staining and varnishing.

Two or three hours later, you can recoat it. I just pop the rag into a zip-lock bag and reuse it. It does make a thin coat, and I usually like to use three or four, but it's so easy and fast, it's not demanding. I sand very lightly between coats with very fine sandpaper on a block, and wip it with a tack rag. The final finish is lovely and smooth.

I like the satin finish. If I can do this, anyone can. I hate to varnish!

Thank you! That's exactly the kind of advice I was looking for!

Make that "wipe it." Since we got going on the "Wythe Blue" thread, I am skittish about mistakes!

I'd check with the paint experts (here or at your store) about this varnish over latex paint - I haven't done that.

I do typically give painted bookshelves (and painted table or chest tops) a coat of Butcher's wax before loading them up, to protect the paint, but only after they've had several weeks to cure. During those weeks, I just put waxed paper on them so I don't have to wait to put the books away.