Learn Spanish (Latin America): El tema es muy claro y tenemos mucho tiempo. - The topic is very clear and we have a lot of time.

This is the key difference between these two words! We use muy (very) right before adjectives, like the describing word claro (clear). We use mucho (a lot of / much) before nouns, like the thing tiempo (time).

Why is it el tema and not la tema since it ends in an -a?

tema is an exception to the normal gender rule. Many Spanish words ending in -ma actually come from ancient Greek and are masculine. That is why it takes the masculine "the", which is el. Another common example you will see often is el problema.

Could I use está instead of es to say the topic "is" very clear?

In this case, no. We use es (from the verb ser) because being clear is a core characteristic or basic trait of this topic. We usually save the other verb for "to be", estar, for temporary states, emotions, or physical locations.

Is tiempo the only word for "time" in Spanish?