Envato authors of WordPress themes and plugins are permitted to offer lite versions (a version with reduced/limited functionality) of their exclusive themes and plugins for free on wordpress.org.
Apart from these key exceptions, there are no other circumstances in which you can make your exclusive items (or related items) available outside of Envato without breaching this exclusivity policy.
So that’s a no on that one.
No. The reason you can give away add-ons on your own site is that they are just to enhance or add to the core item. An HTML or PSD version would be a stand-alone item (not requiring the core item to work), so you wouldn’t be able to sell or give them away on your website or any other site.
To use a gaming analogy… if your item is an PS4 game, then you can give away DLC for that PS4 game, but you can’t give away an XBox version of that game.
Keep in mind that I’m not providing ‘official answers’ as an Envato representative. If I don’t know the answer then I’ll keep my mouth shut and wait for the ‘powers that be’ to address it… but the instances queried so far are pretty clear cut when it comes to the stated rules.