What is the best kit for making 20 centerpieces?

It depends on if you want to freeze all 20 globes at one time or are willing to make, say 5 or 10 at a time. Each lantern requires the use of one freezing base and one balloon. The freezing bases can be used again, so if you have 5 bases, you can make 5 at a time, and so on.

If you want to make primarily small globes, my suggestion would be to buy one Deluxe Pack because it has great directions for making centerpieces and 2 small freezing bases (it has 2 large bases too, but then you could make larger globes for the front door). Then you can buy extra freezing bases and extra balloons to make as many small globes as you want.

Make them ahead of time to make sure they work for the centerpiece that you have created. Do a practice centerpiece if you can. Set it up the way you want it and light it. Does it work? Does the globe slide around? (A piece of white tissue paper in between slick surfaces disappears when wet and will create enough friction to keep a globe where you want it.)

If the globe works for the centerpiece, then put them in plastic bags to store until they are needed. If they have been in a deep freezer or outside under 10 degrees, take them out an hour or so before you need them so they can defrost.