Not sure if you're still looking for an answer, but just in case -- on brushes with particles like this, they will remain the same size no matter the brush size, just cut off in the area the brush tip is. If you look in the options for the subtool, it will have "particle size" a little below the opacity option. Make that bigger or smaller and the actual glitter and whatnot will be resized :)
Of course you can!
If I may ask a little thing: If you like!! you are free to share the results here, or via note. I would love to see it!
But it's no obligation
Good luck with your project!