Complex/Freeform Layouts

Hi all,
I’m evaluating the platform for our projects. I had not too much time to test yet but what I saw, I love it.
Said that, I would like to know how UI works at all. My main fear/concern is if we can extend with user controles not available in standard CUBA controls, and if UI is based on model driven development or you are free to create UI as you want.
Imagine 2 tables (not related between), with a searcher/filterer each one, one beside the other and below a form to create fast notes and a canvas beside to sign with the finger using signature-pad
Makes no sense maybe, but not sure if my example is clear. My idea is to know how flexible is because you know, customers sometimes has super great ideas you have to deliver as they want, and I don’t want to say to my customers something can’t be done (or can be done but needs a lot of extra job because CUBA can’t by default).