Learn Spanish (Spain): En este concurso hay mucho talento. - In this contest there is a lot of talent.

Because talento is a noun, you cannot use that exact structure directly with it. However, if you change it to the adjective talentoso (talented), you could exclaim ¡Lo talentosos que son en este concurso! (How talented they are in this contest!).

If I just want to exclaim 'How much talent there is!', how would I say that?

To exclaim about the quantity of a noun, you use cuánto instead of the lo que structure. You would say ¡Cuánto talento hay en este concurso! (How much talent there is in this contest!).

Why is it mucho talento and not muy talento?

Talento is a noun, so we use the adjective mucho (a lot of) to describe its quantity. You only use muy (very) before adjectives and adverbs, like in muy difícil (very difficult).

Why do we use este instead of esto for 'this contest'?

Concurso is a masculine singular noun, so it needs the masculine singular adjective este. Esto is a neuter pronoun used only for abstract ideas or unidentified objects, never directly before a noun.

Does hay change if we are talking about plural things, like 'there are many contests'?