Well, I don't understand bitcoinfees.21.co and /r/DarkNetMarketsNoobs is too slow I want to order something for approximately 0.019 BTC, and go the Bitcoin exchange -> normal wallet (e.g. Electrum on windows) -> Electrum on Tails -> DNM route.
How much BTC should I purchase for this when I want to buy as little more BTC than I actually need as possible, and set the fee on Electrum to the lowest setting ("Within 25 blocks, 1.80889 mBTC/kb")
I'd say maybe like 1.10 times the BTC?