is it 30/20 plays recommended for your playbook?

It depends on how many plays you are going to run per game. My offense typically runs 70+ plays, so I need to have close to 40 in my game plan so I don't hit overuse.

On defense, if you are running mostly base defensive sets, you don't need many because they won't get hit with overuse.

Maximum is 40/30

Not having at least one offensive play , one defensive play, and a total of 30 plays will get your plan reset. Same as going over the 40/30 limit or scouting more than 10 offensive and defensive plays.

I wasn't aware of the 30 play total limit. Good to know.

Hmm, I always wondered on that one. "What is too little?"

That's vital information.

I wouldn't risk going right to the edge of that overall #, however, now I know where the line is.

It doesn't restrict someone from selecting every available play for a specific personnel set, and then setting the percentage of calls for that set to 0% ... or just setting rules. I've seen games where my opponent calls 8-10 plays all game. If you don't know who, consider yourself fortunate. :)

....is dictated by overuse

Base defensive plays (non-blitz plays) are not subject to overuse, and they shouldn't be. There are too few base defenses, and when overuse was installed, this just meant people were going to blitz more.

The problem with 4.5 is that blitzes are ineffective unless you are run blitzing anyway.