That’s about all there is to it. Duvel might be tough since it’s high alcohol, but worth a shot. Start with 1.010-1.020 starter wort, add some extra yeast nutrient.
If starting from several smaller bottles, have your spray bottle of star-san ready. Spray down the bottle cap and the opener, pour the beer into a glass leaving the last couple ounces, swirl up the bottle, and pour it into your jug of starter wort. Usually by the fourth beer my sanitation practices start to slip, so that’s about the limit. Just keep everything sprayed down each time you open it, or flame the bottle with a lighter, and you should be good.
For a bigger bottle, I’ll get a stopper ready that fits the bottle, pour the beer, and then pour the starter wort into the bottle itself and fit the stopper and airlock. Of course it works best to have the bottle chilled for a few days to compact the yeast cake.
You should have some activity after a day or two. Might take longer if the bottle is old. Just step it up slowly and you should be good to go. For Bell’s yeast, I can usually get a pitchable quantity from a 4-pack of Oberon without stepping it up. But then you have to drink Oberon.