keeping cards mint

I have a Toploader binder that I keep mine in for extra extra protection, and it seems to be a good choice from my POV. Cold storing them is also another option.

If you put them in a normal sleeve and then in a binder, all should be ok!
Another alternative is to put them in sleeves first and then in a hard plastic case, but I only use that for shipping.

grading would be another opportunity

No, but its similar. Basically to cold store something is to keep an area at a constant tempreture. I believe Cally keeps her cards at 15 degrees C, which is ideal.

I double sleeve my cards (put them in a perfect fit sleeve upside-down then in an Ultra Pro deck sleeve right side up) then stick them in a binder or a top loader (depending on the rarity and worth of the particular card).

Double sleeving is great for holos or glossy cards. It keeps dust from getting in the sleeves and causing scratches.

Well I don’t think weight can damage them, but overstuffed binders can. The pages can get stuck under the metal rings and put indents in your cards.