"Ella es una niña."

Yes, a girlchild, never a boychild

Yes. This is one example as to why Spanish can be confusing for those of us who speak English.

In Spanish it is ok to drop the personal pronoun "Ella" when the context is clear. So they both mean roughly the same.

Both are correct. In English, we generally don't apply masculinity/femininity. In Spanish, niña is the feminine version of child. So, saying "Ella es una niña." means "She is a child." with female being implied.

Mostly. Spanish has one extra letter: ñ.

They are different letters. "N" is like the English "N". The letter "ñ" sounds like "en-yay" by itself, but when used in a word it is very close to "ni". For example, "niño" sounds like "ninio".

Espana = es-pa-na

España = es-pa-nia

For a beginner I would recommend pronouncing ñ as an 'ni' sound.

Once you hear the ñ sound a few times yourself you'll learn that its a much harsher noise than just 'ni' but it's a step in the right direction I would say.

It is a girl = Es una niña

She is a girl = Ella es una niña

Because it uses ella, which means "she".

"él" requires an accent when it means "he", and no accent when it means "the". The accent is only there to differentiate the two meanings. "ella" has no other word that sounds like it, so it has no accent in this case.

Sure, you can use it (native Spanish speaker here).