All good tips. Heat and Bond lite is a must. The regular will gum up the needle and you will have a big mess.
I always use a stabilizer, makes a much nicer applique.
I think the onsies made by Carter are to thin. I order all mine online from RustyBumper. They are the best quality and they have about every color you could want.
Applique is one of my most favorite things to do. I love using my embroidery machine to do applique too. I probably have a couple hundred machine applique designs.
This Christmas jumper I did for my granddaughter is all applique, done by hand.