Hey there,
1. No, this is not something that Matukio has build in, but you could use the Joomla ACL system in combination with a subscription component for this. For example here is how we handle subscriptions on our site. If you purchase Matukio our subscription system will add your user to the Matukio user group. User's in the Matukio group have access to only downloads for Matukio. If you purchase a bundle, then the subscription system will add you in all groups - Hotspots, CComment, Matukio - this way you'll get access to all components.
We are using akeebasubs, but it is a developer component and not that user friendly anymore, but there are a lot of other subscription components out there that can do the same.
2. Have you checked in your spam folder. This is normally where the emails land.
3. We have several plugins for offline booking. If the user doesn't want to pay immediately he can select the cash payment method or bank transfer. You are also able to rename the current plugins. So cash could be "pay afterwards" this way it will be maybe more clear for the user that he won't be charged immediately.
4. Matukio generally works with any template. We use the bootstrap framework, so any template that is build on it should look fine. There are always situations where a template is overriding something in the bootstrap framework, that it shouldn't override, but that doesn't happen that often and if it does, then inspecting the element and adding few lines of css solves the issue.
Regards,
Daniel