Please deposit and withdraw BTC (testnet) and ETH (testnet Rinkeby) if you can, trade around and help iron out bugs (if any).
1. Honestly you'll have harder time looking for tester since not everyone have testnet coin. As for myself, i returned few micro tBTC to faucet where i got tBTC after i done experimenting with LN few years ago.
2. Since it's not easy to obtain tBTC in big quantity, you should specify minimum withdraw/deposit amount of your exchange.