I did see you posted elsewhere in the Community as well and I did address your questions there. I'm sorry I did not see this until now. While we don't have phone support available over the weekend, I recommend calling in to our phone support channel when they re-open tomorrow at 8AM ET. If you're looking for a more hands-on approach and want someone to answer any questions you might have while working on the event in real-time. Click here for their numbers and hours.
1) The theme does carry over from what you chose when designing the registration and landing pages. If you choose the "custom" theme you will have a bit more flexibility in changing the look. That said, you should also be able to change the background color of the blocks when working inside of them.
2) You can see what messages appear in the confirmation notifications (and edit them if necessary) by going back to Edit Event. Click here to see where that is and how to do it. I would also note that while the link in a test email does not collect registration information, you can always pull up the event page itself and register with you own email address to see what the notifications look like in real time. And then cancel the dummy registration information if you don't need to register for your own event.
3) When you create an event invite it comes pre-loaded with a lot of the information you filled in elsewhere in the event creation process. It automatically generates a link to your live event in the block that says "Register Now."
I did see you were able to successfully schedule and send event invites. But certainly if you have any more questions you can come back to the Community!