I have an old BK2 that I got a Raven carbon fiber shaft for it and it works great. The original wooden shaft also works great, I just wanted carbon shaft.
There are different opinions on what makes a good break cue.
I like light cues so I can accelerate faster and that works great on “big breaks”. But a heavier cue will work a bit better on a soft break and will produce more power.
So first consider the weight that you want and see what are the options out there.
Carbon shaft will give you durability and will need less maintenance, so that is my choice for a shaft.
As for tip, I would go with a leather break tip. Although I have a phenolic tip on the original BK shaft and on the Raven, I also have a Samsara break tip on a different jump/break cue that I have and it works super, better control without too much loss of power.
The phenolic tip will work best for a softer break in which you can be more accurate.
I always preferred a break cue without a metal joint sleeve, it just felt better and gave a better feedback, but I don’t think that it would make that much of a difference when using carbon fiber shaft, haven’t tried it to form a solid option.
Bottom line, go with what you want, if you found something that you like better then go for it because having it in your mind will hurt your game. So get out of your mind and into your hands, and if you don’t like it, you can always sell and move to something else.
And to be completely honest, I think that with today's racking using the magic rack that keeps everything tight, any cue will do the job as long as the stroke is good and accurate and you can get it to the desired speed, so weight and balance points would be the two main factors for the cue.