I try to look up the specs of pieces as I make them. Lego are actually built around a value of 1.6 mm., so most dimensions of most pieces fall into a sort of a “grid”. I decided to make things easy on myself and have traded mm for m. The distance on a brick (in my model) from one stud to the next is exactly 8 m. easy to move bricks around using inference locking and the Move tool by increments of 8m!
As for the bricks, this is my “virtual pile of bricks”:
Each brick is saved as its own component. Whenever I need a new brick, I select one that is close to the one I need, make it unique, rename it, then make the changes I need.