Pues “Una película: <Batman>”??? Correcto ??

Pues, to say ´best friend´ I could say amiga mía en lugar de mejor amiga ¿

Or did you mean it should have been:
Querida Sasha:
Amiga mía...

I'm not sure what you mean. Could you elaborate?

I wanted to say Ï hope you are doing all the activities that we spoke of before we left¨

So correcto: ...y estés haciendo todas las actividades de las que hablábamos antes de irnos

And, in this context, does ´las´ Clarify the subject of the past discussion as the activities ?

You can say "amiga mía", but this just means "my friend". If you really wanna emphasise that she's you're best friend, you can write it the way I corrected it.

No entiendo, quería decir ¨I feel like I have done nothing¨, so pronominal verb (sentir) changes not reflexive if its meaning is accompanied by a metaphor or technique or hyperbole? Siento -> no he hecho nada.

I wanted to say it has been hot, no?

I know sometimes I am a bit lazy thank you hahaha

De bueno = of good, if I am going to use como + adjective, must I always do cómo + de + adjective?

Kind of, "de las que" is what introduces the relative clause. "Que" is the main particle and, in this case, it goes with "de" because that's the preposition that the verb "hablar" uses ("Hablé de todos mis problemas, pero no me escuchó."). When that preposition is "a", "con", "de", "en" or "por", you can actually write it without the "las" part ("de que"). However, it is very common to include it, because, this way, it cannot be mistaken for something else.

Gracias, pues ;

Cool (colloquial) = guay
Cool (formal) = increíble.
And (conjugated poder) dejar de + infinitive = (to not/permit) action

Thank you

Ok so imperative + attached object you stress the second last vowel. Thnx.

You have to differentiate between "sentir" being used with the meaning of 'I think, my opinion is' and the meaning of 'I am experiencing a physical sensation'.
Your sentence means (as I understand it) "I think I haven't done anything" → "Siento que no he hecho nada".
If you write "me siento", then it's "Me siento como si no hubiese hecho nada", which means "I feel as if I had done nothing", i.e. I don't feel tired at all, I'm not experiencing the physical sensation of tiredness. An example with this meaning: "Me siento como si no hubiese hecho nada, podría correr diez kilómetros más sin problema.".
Does this clarification help?

That's correct, my question is: where has it been hot? If you're friend is on her holidays, I guess she traveled somewhere, right? If this is the case, there are two different locations in your text: the one where you are and the one where your friend is. I'm only saying that it is not clear which one of the two you're refering two. This is just a question of content, not grammar.

So the correct phrasing would be

Una película: «Batman»

Ok so de is a connective and is used here because hablar + de, you must put the direct object pronoun so it clarifies the subject located in the relative clause (hablábamos antes de irnos). You can just write it as de que however de las que makes it more precise, ok thanks !!!

If you're talking about the degree/level of the adjective and want to use "cómo", you must include "de". But that happens in this context, I don't know what you mean by "always".
As I've said previously, don't try to translate from one language to the other, "cómo de" is an inseparable structure, so it's not "of good". Consider this, I see the sentence "It happened because of the rain." and I say, so it is "because of" = "porque de"? Does this make sense?

I wouldn't raise "increíble" to the category of formal, it's just standard.
"Dejar" is one of those verbs that has a trillion meanings, so I wouldn't categorise it so fast. Here it's "she cannot stop doing it", not with the meaning of actual permision/necessity; it could also be written as "she cannot stop doing it because of her enthusiasm", so strictly speaking, it means she doesn't wanna stop doing it.

So sentir has two uses:
1. I think, my opinion is (I feel, not physically) (siento)
2. I am experiencing a physical sensation (physical sensation solely) (me siento).

Yo entiendo gracias :)!!!

Oh lol. We are in the same place (hometown) my bad for being obscure

Ah so it is very ambiguous and can be used in the same way to mean multiple things, but baseline it means (subject) cannot stop thnx

The stress in the imperative doesn't change. This means that adding enclitics ("me, se, lo") can change the accent (capitalised to emphasise): viSIta = visit; if you add the "me" (visit me) → "viSÍtame", now the accent is necessary because it's the third to last syllable. Another example: esCRIbe = write; esCRÍbeme = write to me; esCRÍbenoslo = write it to us.

Unfortunately that is how my brain works I am trying to box in what features I can, i know i’ll make mistakes trying to apply the same rules to similar context but this is how i learn, through similarities and then them being disproven through new logic/info!!! But i understand your reprimand !

Ok I understand count back <- 3 vowels from the end then add accent/stress. But if its both a direct+Indirect attached you do not count the indirect thank you

Quotation marks are used when quoting, so the question here is: Are you citing something? You could argue that it's not a quotation because you're not mentioning it in a full sentence. My personal preference is writing the inverted commas, but you can decide.

You don't have to count, just have in mind where the stress falls in the normal imperative (with nothing added), putting or not the accent is a question of accent rules. For example:
esCRIbe, esCRÍbelo, esCRÍbenoslo → It is always the "cri" syllable, the accent appears because it's the third to last and fourth to last syllable respectively (in these cases the accent is always written). Look at this, however:
escriBID (second person plural), escriBIDlo, escriBÍDnoslo → The rule I said to you doesn't change, it is always the same syllable ("bid") as the one in the imperative without anything added. However, "escribidlo" doesn't have an accent because it is the penultimate syllable and the word ends in vocal, "n" or "s" (e.g. "niebla", but "néctar"). I recommend you check the accentuation rules if you're interested.