How can I route an unknown amount of wires through an outside wall?
You ask for a box, as long as 120V does not go thru, then you can use a low voltage cut-in ring.



These rings come in 1,2,3 and 4 gang or even round.  You can use a 1 gang weatherproof cover with either 1 1/2 hub or 3 hubs.  Or you can buy a blank plate and drill your own 7/8. 

 

Weatherproof plate with 3 1/2 hubs

To make where your cable goes thru the cover you can use a strain relief connector.  You pick your connectors by the size of gland (grommet) you need to use and then there is a compression nut that tightens and the gland compresses to your cable.



You can probably get 2 holes drilled if you use a 1 gang blank plate or 4 holes if you use the 2 gang ring and plate.  You can always do one size and change the ring to a larger size if you want, but you can't go backwards. 

You can buy all this at a DIY box store or at your local electrical distributor.