Moving up from a 4.0 level to 4.5 how to prepare?

you need to work with an instructor, a wall, or a friend someone who steals time type drills, as you move to interclub and see 4.5 and 5.0 players, you need to amp up everything, footwork, preparation, quick reads of the ball, while also softening your hands, etc.

When I've played interclub tennis as a 4.0 player, this is what I encountered. The heavier serves were ok, I move forward and take early/block/swing out etc. at heavy servers, kickers, etc. It wasn't a problem. I wasn't able to move in as aggressively upon my serve, they were masters at putting the return at my feet causing me to lift the ball, and they put away.

the matches went fast and more points won off of angle or put away volleys by all of us, weaker returns, etc.

Years ago, I read that you should try to balance your opponents out, with 1/3 better, 1/3 worse, and 1/3 equal to you in overall skill level.

What kind of game to you want to play?

What are your natural strengths, in terms of tennis tactics, and also your basic personality and physique? By putting those three things together, try to form a game that works best for you.

Whether you want to use a nimble defense, total serve and volley, total baseline attack, or some type of all-court game, as long as you know what works, then you can structure your practice sessions to build a solid foundation.

And, of course, the more shots you can execute well, the better.

Consistency, as you noted, is critical. You must be able to keep your unforced errors to as low a number as possible. Tennis matches are almost always lost [through errors], they are very seldom won by hitting winners.

I frequently talk about serving at 90-95% of your maximum speed, in order to "throw strikes" with your first serve.

If you can get your first serve in @ 80% of your attempts (or better), that puts tremendous pressure on your opponent! OTOH, if your first serve is only going in @ 40%, then YOU will be the one under pressure. They don't call the serve the #1 shot in tennis for nothing.

We have the old saying, "You're only as good as your second serve." You've probably heard that one before :-)

If you're playing doubles, yeah. Serve/volleys/returns are pretty much the three shots you're going to want to step up.