user76508: I know probably everyone give an extra transaction fee, but are there minimum transaction fee that one must pay, and is it based on the number of input transaction (UTXO)?
And I have read that wallet developers tries to eliminate small UTXOs when preparing a new transaction. So is there harm for having too many small/dust UTXOs?

user69241: 
are there minimum transaction fees?

No, you could also pay no fee but your transaction will probably not be included in a block then. This is a pretty old example-transaction with no fee paid: https://blockchain.info/de/tx/8131ffb0a2c945ecaf9b9063e59558784f9c3a74741ce6ae2a18d0571dac15bb

and is it based on the number of input transaction

Not on the number but on the size in Bytes.

So is there harm for having too many small/dust UTXOs?

Yes. You can see it at the moment. People pay around 1.80$ for a "one address to one address"-transaction. More inputs/outputs means a bigger size. Bigger size means higher fees. 

76508: <p>I know probably everyone give an extra transaction fee, but are there minimum transaction fee that one must pay, and is it based on the number of input transaction (UTXO)?</p>

<p>And I have read that wallet developers tries to eliminate small UTXOs when preparing a new transaction. So is there harm for having too many small/dust UTXOs?</p>
 69241: <blockquote>
  <p>are there minimum transaction fees?</p>
</blockquote>

<p>No, you could also pay no fee but your transaction will probably not be included in a block then. This is a pretty old example-transaction with no fee paid: <a href="https://blockchain.info/de/tx/8131ffb0a2c945ecaf9b9063e59558784f9c3a74741ce6ae2a18d0571dac15bb" rel="nofollow noreferrer">https://blockchain.info/de/tx/8131ffb0a2c945ecaf9b9063e59558784f9c3a74741ce6ae2a18d0571dac15bb</a></p>

<blockquote>
  <p>and is it based on the number of input transaction</p>
</blockquote>

<p>Not on the number but on the size in Bytes.</p>

<blockquote>
  <p>So is there harm for having too many small/dust UTXOs?</p>
</blockquote>

<p>Yes. You can see it at the moment. People pay around 1.80$ for a "one address to one address"-transaction. More inputs/outputs means a bigger size. Bigger size means higher fees. </p>
