If you're just mining to hold, and trying to simplify, then the easiest thing you can do here is:
Take payouts at intervals, not constantly and throughout a day. Each payout from the pool to your cold wallet is a taxable event. Minimize them.
You claim as income on your return the USD value of each payout, at the time of that payout, when it arrives at your wallet.
The cost basis of each payout is determined by the USD value of that payout, at the time the payout arrives at your wallet.
You can only claim up to 3000$ per year in capital losses in the United States. You can carry losses forward if you exceed that amount in a calendar year.
Technically, when the USDT hits your wallet up on the exchange that is your first taxable event because you got paid to your wallet on the exchange. When you convert to BTC at that point, while the IRS wants you to report it, I don't usually do that in such a scenario. The IRS treats it like an equity and every time you convert it's like selling one stock for another. It can get to be a real pita if you do a ton of trading and people who are serious about it use software to track that automatically.