Setting aside privacy issues (I am aware of those), and focusing only on future cost savings, how big should my UTXOs be?
You know about privacy and if you do not want to link your UTXOs together in a transaction. If you want your future transaction to be on lowest fee, you need only one UTXO. Set the fee to 2 sat/vbyte and send it all to only knew address. But this is about no privacy.