At a first look i tought that this plugin is a little hard to understand, but if i manage to make some changes will be ok to use.

I want to hide the "Booking options & reservations" shown on "add a listing" page. Enabled booking options must be checked (but invisble.). See image "1.png".

After we hide the options above (make them invisible and checked on add a listing page), the following options must be activated and also invisble on the page:
-Enabled booking options
+add a new option

On the -- Define booking option title ---- Define summary text -- zone, the following options must be checked (but hidden from add a listing's page). See image "2.png":
- Enable option (checked)
- Online reservation (checked)
- Availabilitu calendar (checked)
- Accomodation type (checked)

Time range for this offer - This area also needs to be hidden, and the time range must be set automatically from Start date: today's date , End date + 6 months after today's date.

Availability / Free slots - Calendar - This option is the only option i need to be visible for users on the "add a listing" page, except that i want to have a Calendar where the users only choose the unavailable days (marking them red) with a click of a button.

The price field must be taken automatically from the price on the main field of the form.
The "Textual price / Label under price" must be set in admin panel.
The other fields like Title, Summary, Description, Features, Additional details, Conditions, Limitations, Cancellation policy, position i want to be deleted.

This is all i need for "add a listing" page.

Then i need to modify the approved listing page (visible by visitors on the site). Here i want to hide all the booking options and when i click the button "Send a Message" to the seller i want to open the "Create a reservation" in the popup.

Anyone can make this?

This is the pop-up i want to be opened when i click to the Send Messsage to seller button instead the default send a message form.

Based on your description it sounds you just need few hides via css and then trigger from javascript to open reservatiom box when clicked on send message button.
Or?

Exactly.

@necunoscut
Rightclick on box you want to hide and select "inspect". You will get CSS selector of block.
Then add to your style.css (or appearance > customization > css) code in format:
selector {display:none!important;}
To bind reservation form on button, you must code that feature in JS.