Just a ballpark estimate based on my recipe. Xylitol= 1/4 tsp. Glycerin 1 tsp (or slightly less). Mix the glycerin with a little bit of water.
As for dextrose, you can use any sweetener such as sucrose, honey etc but it'll contribute to tooth decay. The sodium propionate is used as a preservative. You shouldn't need it, the glycerin has the same effect.
If you are using the Xylitol as a sweetener you might want to increase increase it to maybe a 1 tsp.
I'd recommend adding the xylitol to a little bit of water to help dissolve it, then add the gylcerine.
A tsp of salt seems excessive. Maybe start out with a 1/4 tsp.
It really all depends on your personal tastes. Just keep notes and make adjustments along the way.