Where can I find the number of UTXOs my receiving address contain ? Is there any website ?
You can be able to see your inputs on most wallets. But to make it easier, use wallets with coin control. Wallets like Electrum and Bluewallet.
If I reuse an address to receive bitcoin will it count as a second UTXO ?
Yes. If you use an address to receive bitcoin two times and you want to spend the coins or part of the coins from first and second UTXO, it will have 2 inputs and the more the fee.