1. If you are using a none .heliohost.org domain, then you will need to add ns1.heliohost.org and ns2.heliohost.org as your nameservers as soon as you can after signup. This can be done from your domain registerer's control panel.
2. Yes, we offer cPanel - an award winning control panel with most of the features you could want! Click here for a demo.
3. If you signup now, you will be placed on Stevie. At the moment, all accounts are being hosted on Stevie. However, we are currently configuring our new server, Charlie (and Johnny and Cody), which is currently hosting the official HelioHost and HelioNet websites. Signups to Charlie will be opened in the next few months.
4. You are limited to 250MB of disk space, and have unlimited bandwidth! However, you mustn't take up too many server resources or abuse the servers otherwise your account will be suspended.
Hope this helps!