Noventa es más que ochenta.

Es is the verb ser (to be) in the él/ella/usted form.

In Spanish, a number word like noventa can act as a singular noun-like idea, so Spanish uses es:

• Noventa es más que ochenta.

Literally, this is like saying Ninety is more than eighty.

You usually do not omit es here in a normal sentence. Spanish needs the verb.

When Spanish compares one thing directly with another, it normally uses:

• más ... que = more ... than
• menos ... que = less ... than

So:

• noventa es más que ochenta

That is the standard comparison pattern.

Más de is used in other situations, especially with amounts like more than 20, more than a year, etc.:

• más de veinte personas = more than twenty people

So in this sentence, where one number is being compared with another specific number, más que is the expected choice.

The accent mark is important.

• más = more
• mas = but (a literary or old-fashioned word)

So in this sentence, it must be más with the accent, because it means more.

Examples:

• más dinero = more money
• Quise ir, mas no pude. = I wanted to go, but I couldn’t.
  (This mas without an accent is uncommon in everyday speech.)

A simple Latin American pronunciation guide:

• noventa → noh-BEN-tah
• es → ess
• más → mahs
• que → keh
• ochenta → oh-CHEN-tah

A few notes:

• In much of Latin America, v in noventa sounds very similar to b.
• que is pronounced keh; the u is silent.
• The stress is:
  • noVENta
  • MÁS
  • oCHENta

Spanish number words usually appear without articles when you are simply naming or comparing numbers.

So:

• Noventa es más que ochenta.

That is normal.

Using an article would usually change the meaning or sound unnatural here. For example, articles may appear in special contexts, such as referring to:

• a decade
• a highway or route number
• a page, room, bus line, etc.

But for plain numerical comparison, no article is needed.

Yes. Mayor que can also mean greater than, especially in mathematical or more formal contexts.

So both are possible:

• Noventa es más que ochenta.
• Noventa es mayor que ochenta.

A useful distinction:

• más que = common general comparison, more than
• mayor que = often used for size, age, rank, or mathematical greater than

If you are talking specifically about numbers in a math-like way, mayor que is very natural.

By themselves, these cardinal numbers are generally not changing for gender.

• noventa libros
• noventa casas
• ochenta dólares
• ochenta sillas

The number stays the same.

A major exception in Spanish number agreement happens with uno and forms based on it:

• un libro
• una casa
• veintiún libros
• veintiuna casas

But ochenta and noventa do not change for gender.

Yes. You can write:

• 90 es más que 80.

That is understandable and correct.

In ordinary prose, Spanish often writes smaller numbers as words, but numerals are also very common, especially in:

• math
• charts
• exercises
• informal writing

So both forms work:

• Noventa es más que ochenta.
• 90 es más que 80.

They are historically related, but Spanish number formation is not always perfectly transparent.

Compare:

• ocho → ochenta
• nueve → noventa

These are the standard forms and must simply be learned as vocabulary.

This is similar to how English has:

• eight → eighty
• nine → ninety

The connection is there, but the forms are not completely predictable from the basic number alone.

Normally, no. Number words are usually written in lowercase:

• noventa es más que ochenta

In your sentence, Noventa is capitalized only because it is at the beginning of the sentence.

So the normal rule is the same as in English:

• capitalize at the start of a sentence
• otherwise, use lowercase unless there is some special reason

Yes, but the original order is the most straightforward.

Standard:

• Noventa es más que ochenta.

You might also see other ways of expressing the same idea, depending on context:

• Ochenta es menos que noventa.
• Noventa es mayor que ochenta.

Spanish is somewhat flexible, but for a simple learner sentence, Noventa es más que ochenta is clear and natural.