If I want to use BTC to buy into this ICO, what do I put for the "BitCoin wallet the payment will come from:" section? I Know how to generate receiving addresses, but How do I find out my sending address? Using Electrum btw
You can see you addresses on the "Addresses" tab of Electrum.
If you have one address with a non-zero balance only, then specify it.
If you have more than one address with a non-zero balance - yes, the sending (payment) addresses can be more than one too. In this case, specify the address with more balance. After receiving the confirmation e-mail, contact the team by e-mail and describe the situation. I guess they will ask you not for the address, but for the transaction hash. Or they will provide you separate address for your investment. I didn't invest in btc, so I'm not sure.