Standard network Setup

First, define "redundancy" in the context of what you intend to accomplish.

Here is an example of what I would call "full redundancy":

"Separate switches and routers and firewall throughout.  Separate cable runs in different physical locations in the building backbone.  Two internet connections which arrive using different physical mechanisms and through different physical routes from two different ISPs."

This would be for one site/building.  
Then you could consider having a separate site for backing up the whole thing.

Given this, you could back off from some of it if it seems to make sense to you.  Only you can decide what makes sense for your situation.  What kinds of failures, threats and vulnerabilities are you wanting to address?  

Example in your case:

Using more than a single fiber for intra-site communications would make sense if the concern is failed switch ports, failed switches, etc.  This implies that those added switch capabilities are also present.

Using more than a single fiber with the fiber runs in different physical locations for intra-site communications would make sense if physical damage to the runs is the concern.  In this case, the redundant switches might also be in separate locations.

If you eliminate physical damage as a likely vulnerability (e.g. a localized fire or a fully-involved building fire), then you get back to failed electronics and failed internet service pretty much.