Some doubts..

Are "a" and "per" exactly the same?

They are the same. "per' is generally used in science or statistical sentences. "a" is common usage.

3) Does Are “how’s” and “house” pronounced the same?

"How's" sounds like 'howz'. "House" the noun sounds like 'howse'. 'House" the verb sounds like "hows". Link to a recording of the pronunciation is below.

http://dictionary.reference.com/browse/house

4) Idem with “Hertz” and “hurts”.

The same sound. In fact, the dictionary says pronounce "hertz" like "hurts".

http://dictionary.reference.com/browse/hertz?s=t

1) Having this sentences: "I sleep 7 hours a night" and "I sleep 7 hours per night".

"A" and "per" are not exactly the same. Per is proper when dealing with quantity like "4 dollars per box", or "3 times per hour". A is used when dealing with 1 thing or object as in "I have a nice car". Both "I sleep 7 hours a night" and "I sleep 7 hours per night" are correct sentiences. However in proper english a is more "slang", and per is proper english when dealing with quantity.

I guess "per" is less used.

per is proper english when dealing with quantity.

2) Is “He never washes his car” right?

Yes "He never washes his car." is right

4) Idem with “Hertz” and “hurts”.

Hertz is a unit of sound, hurts is a unit for pain.

Hi, I'm reviewing basic stuff and I've some troubles with these points:

1) In these sentences: "I sleep 7 hours a night" and "I sleep 7 hours per night".

Are "a" and "per" exactly the same?

Yes.

I guess "per" is less used.

No, both are common.

I mean is "-es" used with "never" too?

Yes, definitely. When the subject is 'he', the verb normally needs '-s'.

3) Are “How’s” and “house” pronounced the same?

"How's" is pronounced with a 'z' sound at the end. When "house" is a noun (=casa), it is pronounced with an 's' sound at the end. When "house" is a verb (=alojar), it is pronounced the same as "how's".

4) Idem with “Hertz” and “hurts”.

Yes, in English (though "Hertz" is a German word, of course!).