Unknown sSpaces

To be honest, I have already thought about aliens.

I imageined howwhat they could look like and overall what kind of overall perception they have on life.

We either say "what sb./sth. looks like" or "how sb./sth. looks".

And I aksked myselvef if they are more or less intelligent than human beeings.

Thinking about it, it would be difficult to define that, because we would mesure their intelligence with human tools.

So what gives us the right to decide Iif other living beings are more or less intelligent than we are, Iif they live in a totally different reality?

I actually don't know for certain if I would try to communicate with them.

You're sentence is perfect, but seeing what you wrote in the next sentence I add this so it flows better.

IBut in the end I would do so, out of curiosity.

I would describe humanity, including pictures of people from different parts of the earth and from different ages and professions.

I would describe our need to sleep and fight wars, and our need to be loved and longing for loving someone else and our need to be loved.

But I would keep in mind that this could be also dangerous, because if I telling them about all of the "human insights", it could be pretty easy for them to take over the world over.

If aliens would exist, I would be super excidetted about their answeres to this message.

Maybe we could learn a lot ofrom them.

To be honest, I've already thought about aliens.

"already" is generally used with the perfect tenses.
In speech we might drop the "have", but not often in writing.
The website below gives some good examples, but also explains that words like "just", "yet" and "still" are, in most cases, used with "I have..."/"I had..."
https://learnenglish.britishcouncil.org/grammar/b1-b2-grammar/just-yet-still-and-already

I imageined howwhat they could look like and overall what kind of perception they have on life.

Generally we use "what" questions for things linked to an object/person directly.
"I wonder what it tastes/sounds/looks/smells/feels like."

"How" questions cover two major areas in English:
1. The method used to do something
How do I make coffee?
How can we buy a train ticket in the trainer station?

2. To ask someone who knows the information to pass it on to us (the speaker)
Person A (Never eaten curry): How does curry taste?
Person B (has eaten curry): It tastes nice, very spicy.

Person A (Didn't visit her friend in the hospital) How does he look?
Person B (Visited her friend in the hospital): He looks okay, but he has a cast on his broken arm.

Person A (Doesn't speak German): How do you say "hello" in German?
Person B (From Hamburg :P): In Hamburg we say "Moin!", but you can also say "Hallo".

What matters to them, how? How do they define a successful life.?

They should both be questions, they are in this case unanswerable, but that is okay.

Because tThese questions are already big onesso big for us humans.

Avoid using "and", "but" and "because" at the beginning of a sentence, in most cases it's not so much a grammar problem, but it isn't necessary in English, the sentence has the same meaning without.

And I aksked myselvef if they are more or less intelligent than human beeings.

myself (singular ALWAYS)
herself/himself (singular)
themselves (plural [either gender])

Thinking about it, it would be difficult to define that, because we would measure their intelligence with human tools.

So wWhat gives us the right to decide Ifwhether other living beings are more or less intelligent than we are, Iif they live inhave a totally different reality?existence.

Sorry I changed the last part a lot :P.
The context is you know "nothing" about the aliens, so you wouldn't know what the differences would be either, reality, environment, dimension, etc. to cover ALL of these I would go with "existence".

Also, I changed the first "if" to "whether"
If = conditional, but you already have one of those with "if they have a totally different existence" [In German: wenn]
Whether = two alternatives are possible, "more or less" in this case means we should use "whether" [In German: ob]

I hope you don't mind the German.

In the end I would somight, out of curiosity.

can't have the sentence before and then in the next one say the direct opposite. You can however say that it would be a possibility or likely using "might"

I would describe humanity, including pictures of people from different parts of the earth and from different ages and professions.

from different ages = different periods of time, for example: stone age, bronze age, industrial age, etc.
of different ages = people at different stages of their life 20 years old, 50 years old, 100 years old, etc.

I would describe our need to sleep and war, and our need to be loved and longing for lovingto be loved (by someone else).

You don't need the "by someone else" because it is implied, but aliens might not know that, so it could be left in :P. Grammatically it isn't a big deal.

But I would keep in mind that this could be also be dangerous, because by telling them about all of the "human insights"civilization and culture, it could then be pretty easy for them to takeover the world over.

"also" before the "main verb" in most cases.

I have also made coffee to share with the aliens.

If aliens would existed, I would be super excidetted about their answeres to this message.

Don't put "would" in the "If" side of the sentence. It can be possible, but honestly, I teach English and very very seldom see it.

If I eat a lot, (then) I will feel sick.
If ...[Present verb]..., (then)... will [infinitive without "to"]...

If I ate a lot, I would feel sick.
If ...[Past verb]..., (then)... would [infinitive without "to"]...

If I had eaten a lot, I would have felt sick.
If ...[past perfect tense]..., (then)... would [present perfect tense]...

Those are the most important 3 conditionals, they always follow the same structure, you can find a better breakdown here, but don't go crazy with it, your English is good and you will learn to use them automatically as you learn more.

https://www.englisch-hilfen.de/en/grammar/if.htm