I have to look at this with calm, but I'll be back to it.

For the time being I'll tell you that "por qué" is fine, you can leave it. It is your direct translation. I just said "para qué" sounds better (to mi) . I think I gave it to you with question mark.

"No quiero verte sufrir..." is better.
In the fourth verse of this stanza you have a typo: "es" = "se".
"Ven" repeats. Check it out.

No sé. Maybe because we use it more, seems to be more comnversational... "What for" will be the meaning. "What are you going to get by doing so...?" No rule. It has nothing to do with "por and para".

Now, let's see:
The subjunctive is a possibility, not a fact. It goes preceeded by some verbs that imply that possibility, such as, "querer, desear, esperar, preferir" + "que":
"quiero que vengas/espero que vengas..." etc.
Or preceeded by impersonal expressions such as, "es necesario, es imposible, es
mejor" + "que":
"es necesario que vengas/es mejor que vengas..." etc.
The present subjunctive is formed from the first person of the indicative present (in case it is irregular), having in mind the conjugation (-ar, -er/-ir) to change the "a" to "e", or the"e/I" to "a":
"hablo (regular -ar) --> hable"
"tengo" (irregular -er) --> tenga"
"paso" (regular -ar) --> pase, pases, pase, pasemos, paseis, pasen.
The word you wrote "pasare" doesn't exist. If you put an accent and say "pasaré", will be future.
Look at "Lo que pasare mañana" and see if it adjust to these charactheristics.
The idea is that "something will happen tomorrow", that's for sure, the only thing he doesn't know is "what".
"Debe haber" (must be) is an impersonal expression, has nothing to do with subjunctive.
The "if" (si) clauses don't work in subjunctive with the present tense, only with imperfect subjunctive:
"Si tengo dinero, ire", (present-future)
"Si tuviera dinero, iría", (imperfect subjunctive-conditional)

If these explanations are clear, save them and work with them. Try to use them.

"Verte hacer daño" means to somebody else. I told you "sufrir" is better than "sufriendo" because of what comes after.
'I'll explain "por and para" some other day.

You can use that site for the tenses, they are correct. In regads to future subjunctive, I told you it doesn't exist too fast. It does but it's not in use.
Have in mind that with the example I gave you, in present, you are expressing possibility in the future, and that's what is in use nowadays. Example:
"Quiero que vayas al mercado y compres patatas." "Esperamos que reciban nuestro regalo.

Look at this other one, with "cuando" = "When/whenever":
"Cuando vaya a España, visitaré a mi abuela".

Read this, from the web. See if you understand it:

El futuro simple de subjuntivo tiene un uso muy restringido en la lengua hablada, donde en gran parte ha desaparecido siendo un arcaísmo reservado a textos más formales, particularmente textos jurídicos.
Example: Quien incumpliere esta regla, será sancionado

Hasta mañana. Espero que lo digieras bien!

Aquí tienes un Viejo refrán:

"Donde fueres,
haz lo que vieres"

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