You can buy anything with crypto. If it's not a direct wallet to wallet tranaction- there will have to be an intermediate that does the conversion, but it's no different than paying an overseas seller on Ebay for instance. In that case, the dollars get converted to whatever the overseas seller wants it in, and you pay a fee for that.
Same deal. There are services that will convert crypto into dollars for the purchase. Fees are high for a small purchase though, it's not a fixed %- so you won't be using a conversion service to buy a taco.
I'd sell my Gen 1 for 0.82 BTC.
