Learn Italian: In quanto esperto, il tuo consiglio sarebbe molto utile. - As an expert, your advice would be very useful.

When using in quanto to express a role or capacity (meaning "as" or "in the capacity of"), Italian drops the article entirely. You simply use in quanto plus the bare noun.

Could I use come instead of in quanto here?

Yes, Come esperto is also perfectly correct and means the same thing. In quanto is slightly more formal and emphasizes the logical connection: it is specifically because of their capacity as an expert that the advice is useful. Note that come used for roles also drops the article.

If I am talking to a female expert, does the phrase change?

Yes, it must agree with the person's gender and number. If speaking to a woman, you would say In quanto esperta, and for a group, In quanto esperti.

Why is consiglio singular when the English translation says "advice"?

In English, "advice" is an uncountable noun, but in Italian, consiglio is countable. You use the singular il consiglio for a single piece of advice, and the plural i consigli for multiple pieces of advice.