One common practice to add variety to a grid of CMS content is to split the grid into several Collection Lists.
For example, start with a Collection List (CL) limited to 3 items from 1 to 3, and use Flexbox to make 2 columns followed by an full width item. Then add a new CL, limited to 4 items from 4 to 8, and make a four columns layout. Then a CL with 2 columns with 2 items from 9 to 10, then one with a grid a 2 x 2, etc…
You’ll get a nice list and you can control what is shown and where quite easily.
Now to have that “random feeling”, use the technique above to build a straight grid, made of a series of CL (it ultimately can be 1 CL by item… You’re limited to something like 20 Cl per page), and play with Position (ie relative and top and bottom values to moke them vertically) to introduce your random effect.