Officially, it's not legal in Eternal MTG formats - namely Legacy, Vintage, Pauper, and Commander
The cards on the reserved list are all older, and so their effects tend to be odd or lacking precision
Whether you double- or triple-sleeve your cards comes down to personal preferencebut if maximum protection is your goal, both options offer excellent defense
Aethergeode Miner : Creature (Dwarf Scout), casting cost of one generic and one white mana, 3/1
If Lion Sash is attached to a creature, that creature gets +1/+1 for each counter on Lion Sash
If you just want the tl;dr and my bottom-line assessment: MTGProxy is one of the better sites out there to order from they have tons of ordering options, reasonably fast shipping, and very solid card quality