What is the best way to prepare layout for Magento2?

Question

css

I apologize if the question is somewhat chaotic, but the fact is that I myself cannot absolutely clearly define the problem and how to solve it.
The essence of the problem.
4 people in the team - 2 on the frontend, 2 on the backend - the task is to create a theme for magento2, the theme is based on the default blank theme for M2.
My task at the first stage looks the most primitive - routine - to make up pure html from layouts with styles prepared for Blank and easily modified and pass it all along the hierarchy.
Always before, if there were no special requirements, I organized the layout quite simply - I took a starting template, for example, OptimizedHTML 4, and quickly assembled everything I needed.
I feel that this approach is not ideal in the case of magento layout. For example, out of habit, I use the Sass syntax, and the Blank theme is all in less by default. Well, accordingly, the one to whom I am transferring requires transferring to less, and even so that the default variables correspond to the default theme variables.
I don't know how correct this requirement is, but that's how it is. Actually, it would be possible to stupidly convert all the necessary sass files to less and transfer them. Well, here I also have 2 plugs. 1st - I did not find (perhaps I was looking badly) the optimal solution for converting sass (not scss) to less - for example, sass2less correctly converts only scss, in sass it only changes the signs of variables and that's it.
2nd - I would like to transfer only 1 less file at the output, I'm also not sure that there is a plugin that would produce one less from a heap of sass, well, like one compiled css.
In addition, I understand that you need to master template engines, since this is a web shop, which means that it is a rather large project and there will be a very large number of repeating parts in it. So, you need to organize everything from the very beginning so that later you don’t get lost in these wilds. And here, perhaps it would be better to use not one but different style files ...
In general, I feel that I am confused here, therefore, whoever has experience or correct advice, I will be grateful.