Hi,

Custom Layout
You can use the class of bootstrap directly to Oddo as per your need.
for example:-
  <div class="row container">

                    <div class="col-12 text-center">

                    //content here

                    </div>

</div>
2. fields/tabs to appear conditionally
You can use attrs on the field/tabs as per your need. for example:-
         <field name="name" attrs="{'readonly': [('active', '=', False)]}"/>

         <notebook attrs="{'invisible': [('active', '=', False)]}">

//tab content

           </notebook>

Hope it helps