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 some wallets with coin control. Wallets like Electrum.
If I reuse an address to receive bitcoin will it count as a second UTXO ?
Yes. If you use an address to receive coin two times and you want to spend the coins, it will have 2 inputs and the more the fee.