Some three mana counterspells do see play in the cube, mostly this is down to the distinctly finite number of unrestricted hard counter magic you can find for two mana and not because the cards themselves are super good
In addition to the cards themselves being highly thematic and sticking very closely to Fallouts deep lore with cards named V.A.T.S., Overencumbered and Dogmeat, Ever Loyal, for example there will also be numerous special cards that take advantage of Fallouts rich history too
For brushes you can use anything that would like, the type of brush is up to your taste, as there is no specification on it
Sorcery-speed destruction of creatures with power 3 or greater is available for less mana, and being an enchantment doesn't justify the increased cost
Each combination is identified by the single color it excludes, such as Sans Green or Sans White, and they appear most often in Commander
You can make all your creatures deadly by granting them deathtouch when they attack