1) As with all proper sites - we use 2FA and preserve anonymity but we'd like users to register with an email when signing up. How much of a barrier is this for you guys?
Email is a tiny barrier. But it depends on the number of text boxes you need to type. People like to be lazy on the web
Give the users are choice. Make alternatives : email login, BitID login, sms login, bitcoin payment login (?).
2) We have no min deposit or withdrawal but are thinking of incentivizing people to keep small sums on deposit by offering an interest rate. Would this work for you?
How much interest do you get for putting money in your site?
4) We're API based and would love to see several bots coming in. We'll even give out sample code to people who express interest in it. How valuable is this?
This is a good promotion for your site. How would a developer get money, if users decide to use his bot which connects with your API?
5) Should the site be as sterile as possible or can we be a little more playful with music and art?
Again, give users a choice. Some users may use the site 30 minutes, while others use it for 5 hours straight. Depending the situation a different layout will be preferred.
Say on/off option for music.