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Thanks for asking.
First; is it possible to launch 2 behaviours. Like starting safari and activating virtual mouse at once and then have the vm to disable once another application is started?
Every button press needs a destination, and in Remote Buddy that's the active Behaviour. Since it's usually not desirable that a single button press is followed by the execution of two different actions, there can only be one active Behaviour at a time.
That doesn't mean you can't switch between them, though. In the case of Safari, when you launch Safari, RB automatically activates the Safari Behaviour. You can then switch to the Virtual Mouse either through the RB menu or - with default settings - a long press of the Menu button. You can then use the Virtual Mouse to do anything you want. When you're done, you can perform a long press of the Menu button again and Remote Buddy will figure out what Behaviour it should automatically activate. If Safari is still the active OS X application, that'll be the Behaviour it'll switch to. If the active OS X app is Plex, RB will select the Plex Behaviour.
Second; I was trying to create my own actions and behaviours but found out that I cannot use RB's built-in actions in custom behaviour? When creating new action there are some RB-actions that I can call but not all of them (e.g. my list was missing mac blu ray player) are present.
Not all actions are available globally. Many are only available in the context of the Behaviour that contains them because they f.ex. require the app that's controlled to also be the active OS X app.
You can, however, add your own actions to any existing Behaviour and build on what's already there that way. You can do this by selection "Custom actions…" from the action selection popup at Prefs > Mapping > [Behaviour you want to extend]
