Payment and coins

Bitcoin and Monero. Use Monero if privacy is any part of why you are here, because it is the coin that keeps the payment off a readable public ledger. Use Bitcoin when a vendor takes only Bitcoin and you have no choice, which still happens.

The deposit address is generated fresh for each order, so you are not reusing an address and you do not have to think about the bookkeeping. Fund the order, and the coin sits in escrow until you close it out.

For a first purchase the atlas advice is to keep it small, keep it cheap, and use it to learn the flow rather than to stock up. The coin you can afford to lose on a learning order is the right size for a learning order.