Too many?
N+2 where N is the current number you have.
The appropriate number?
N+1 where N is the current number you have.
As for a real answer to your question.
Overall, for me personally, there really isn't an "appropriate" number. I've gone through a lot of different "phases" where I have focused on different things. Hunting, long range rifle, tactical rifle, IDPA/IPSC, etc. On and on and on...
Between the fun/challenging aspects of it all, the obvious practical benefits (self defense, food procurement), and all the rest of it, the collection has grown over the years. I've got stuff that I haven't shot in years, hell, I actually have some stuff that I have never shot.
There are a few that I have sold in the past, and out of them, I regret selling all but 2 of them. So, now they just get kept and stored...