Is there a limit to how many things you can on a cyberlimb, like the holsters and slides and whatnot? If so, how do you find the values that determine how much it can hold and how much each thing takes up.

There's capacity rules just for this.
Every full/partial limb gives a given ammount of capacity.
Every add-on to this arm EITHER takes up essence OR a certain ammount of Capacity.
Also GM's stopping such nonsense as building hydraulic jacks into arms for example.

Where are they though? I can't seem to find anything about this in the books.

Usually in the Cyberlimb Sections of the Corebook or the Cyber/Bioware Book O.o
What Edition are you talking about?

4e.

4e.

Edit: Sorry for the double post. It wasn't loading and I clicked post like three times.

$R4.5 page 343

XD. Can't believe I missed that. Thankie.

NP.
Also check Augmentation.
Cyber-Limbs actually are almost worth it with the stuff in there . .