How to approach digital electronics questions
The Art of Electronics (first edition anyway) noted that in designing, there are:

"...a few laws of physics, a few rules of thumb and a very large bag of tricks".

What you are asking falls into that bag of tricks that are easily findable, but require experience to understand.

All the questions you ask are easy to implement, if you have the necessary experience, which from your question, you do not appear to have.

We design by looking at the various requirements and looking at various ways to solve it; how we solve it is largely based on experience which a solid grounding in electronics yields.

I suspect each of us has their own approach.