One of the most important things to be aware of is that paint is formulated for either interior use or exterior use, and they have different properties: Interior paint is formulated for: Scrubbability and stain resistance; Good hiding ability; Splatter resistance; Easy touch-up. Exterior paint is formulated for: Color retention; Resistance to fading; Flexibility to withstand expansion and contraction due to weather; To provide a mildew resistant coating; Resistance to tannin bleed. Don't think that you should use exterior paints indoors on the assumption that it is "tougher". In fact, some of the highest-grade exterior paints can be worse to use indoors than a lower-quality interior paint.
As a rule, you should fertilize at least three times a year; spring, summer and early fall.
To keep sanpaper discs from curling up, make a simple jig to keep them flat. Cut out two pieces of 1/4-in. plywood that are slightly larger than the discs. Drill a 1/4-in. hole through the center of each of the pieces. Insert a bolt through one piece, lay the discs on it, and follow up with the second piece. Fasten the stack with a 1/4-in. bolt and wingnut.
Perennial mints, including spearmint, applemint, and peppermint, are very vigorous and can become invasive. Rather than planting them directly in the garden, grow the plants in containers, then sink the containers into the garden. This will contain the roots and limit spreading.