The first is to use online price guides, which can give you a rough estimate of your cards value based on its condition and rarity
Cards like Sol Ring, Command Tower, and Arcane Signet are usually a guaranteed reprint in Commander-focused sets, as are dual lands like the Theros Temples (Temple of Abandon, Temple of Deceit, Temple of Silence) and the Snarls from Strixhaven (Necroblossom Snarl, Furycalm Snarl,Frostboil Snarl)
Just be warned, at $25, Valakut, the Molten Pinnacle suddenly becomes a juicy reprint target for a future Masters set, and it could even be safe for Standard assuming there's no obvious combo pieces (like Primeval Titan)
Honestly, the downside of skipping your draw step on Necropotence is laughably irrelevant
The mulligan guide covers keeping hands with the right counter mix