I am not an expert or a native French speaker, so I can only say what I’ve learned from studying French as a foreign language.

Liaison does not occur in all contexts. Whether or not it can occur depends on the part of speech of each word, and how the words relate grammatically.

In all the guides to liaison for learners that I’ve read, liaison after singular nouns is classified as “forbidden.” (e.g. see “Spell and Sound“, french.about.com) It may occur in some set phrases, but it is wrong to use it outside of those. This is probably the most important point to remember.

It seems liaison can occur before “à” if the preceding word is the adverb “bien” or a verb, but this is optional. Liaison after verbs aside from “est” is rare in any case. Simon Déchamps left a comment giving the following examples where speakers commonly make liaison before “à”:

Bien à vous, viens à moi, aller à la plage, je vis à Paris…

According to Gilles, “viens à moi” is a bit of a set phrase, so some speakers may make liaison here while not making liaison after other verbs such as “aller” or “vis”.

Liaison of the plural suffix after a plural noun (resulting in /z/) is possible in some contexts, but not all. I’m not sure if it would be able to occur in this particular circumstance.