UTXO's

What is the optimal size for a UTXO to be coinjoined?

What is the largest UTXO that can be coinjoined?

Why does the conjoin produce an UTXO that has a low anonymity set yet is to small to qualify for further coinjoins?

If I send btc to wasabi from ledger or trezor, will it show up as one UTXO regardless of how much is sent?