the Swan/FinCEN issue shouldn't matter in the long run

if you plan on ever selling your BTC back into bank money, mixing dormant UTXOs is pointless anyway

get your fiat bitcoin on swan and just keep it as is, and get your LN/el-salvador/silk-road BTC from different sources

in general, it's a good practice to get your bitcoin for different uses from different sources, and keep them in separated wallets