Learn Hardcore German: Wir treffen uns vor der Musikschule. - We are meeting in front of the music school.

Literally, wir treffen uns is we meet ourselves, but idiomatically it just means we meet or we’re meeting (each other).
With people who arrange to meet, German normally uses sich treffen (reflexive), so you almost always say Wir treffen uns, Wir treffen uns morgen, etc.
You would use plain jemanden treffen (to meet someone) when you randomly run into someone or when you emphasize the other person as an object:

Ich treffe meinen Freund. – I’m meeting / running into my friend.
Wir treffen uns. – We’re meeting (each other) / We’re getting together.

Why can’t I just say Wir treffen vor der Musikschule without uns?

treffen almost always needs an object: you meet someone or each other.
So you need either:

a direct object: Wir treffen Anna vor der Musikschule. – We’re meeting Anna…
or the reflexive pronoun: Wir treffen uns vor der Musikschule. – We’re meeting (each other)…
Wir treffen vor der Musikschule is incomplete and sounds wrong to a native speaker.

Why is it vor der Musikschule and not something like bevor der Musikschule?

vor is a preposition meaning in front of (place) or before (time). It is followed by a noun phrase: vor der Musikschule, vor dem Haus, vor dem Essen.
bevor is a conjunction meaning before that introduces a clause with a verb: bevor wir essen, bevor er ankommt.
So:

Wir treffen uns vor der Musikschule. – place: in front of the music school
Wir treffen uns, bevor die Musikschule öffnet. – time: before the music school opens

Why is it der Musikschule and not die Musikschule after vor?

The basic form is die Musikschule (nominative, feminine).
vor is a so‑called two-way preposition; it takes either accusative or dative, depending on meaning:

dative = location (where?)
accusative = direction/movement (to where?)
Here it’s a fixed location (where are we meeting?), so it uses dative:
die Musikschule → der Musikschule in the dative singular.

Could I say Wir treffen uns vor die Musikschule?

No, not with the meaning We’re meeting in front of the music school.
vor + accusative (vor die Musikschule) would describe movement to a position in front of the school, e.g.:

Wir stellen das Auto vor die Musikschule. – We are putting the car in front of the music school.
For a static meeting place, you need dative: vor der Musikschule.

Why is the article der here feminine dative and not masculine?

The word Musikschule ends with -schule, and Schule is feminine: die Schule.
So Musikschule is also feminine: die Musikschule (nominative).
Its dative singular is der Musikschule, not dem Musikschule.
Masculine or neuter nouns would have dem in the dative (dem Mann, dem Haus), but feminine nouns use der.

Why is Musikschule written as one word and not Musik Schule?

German likes to form compound nouns by joining words: Musik + Schule → Musikschule.
A Musikschule is a specific type of school (a music school), so it becomes one new noun.
Writing Musik Schule would look wrong; it would seem like two separate words instead of a compound.

Is there a difference between Wir treffen uns vor der Musikschule and Wir treffen uns an der Musikschule?

Yes, there’s a nuance:

vor der Musikschule strongly suggests in front of the entrance / outside, literally in front of the building.
an der Musikschule is more like at the music school and is a bit vaguer; it could be outside, somewhere at the building, or just generally at that location.
Both can be used to arrange a meeting, but vor der Musikschule is more precise about being in front.

Can I change the word order and say Vor der Musikschule treffen wir uns?

Yes, that’s perfectly correct and common.
German allows you to move adverbials (like place and time) to the front for emphasis or style:

Wir treffen uns vor der Musikschule.
Vor der Musikschule treffen wir uns.
When you put vor der Musikschule first, the verb treffen must stay in second position, so the subject wir moves after the verb: treffen wir.

Why is the verb in the present tense when the meaning is future (a planned meeting)?

German often uses the present tense to talk about the near future, especially for planned events and arrangements, just like English can:

Wir treffen uns morgen vor der Musikschule. – We’re meeting tomorrow in front of the music school.
You could also use future I (Wir werden uns treffen), but it sounds more formal or emphasizes the futurity. In everyday speech, the simple present is normal for arrangements.

What’s the difference between Wir treffen uns and Wir begegnen uns?

sich treffen is typically intentional: you arrange to meet.
- Wir treffen uns vor der Musikschule. – We’re meeting (by arrangement) in front of the music school.
sich begegnen is usually by chance: you run into each other.
- Wir begegnen uns oft vor der Musikschule. – We often run into each other in front of the music school.
  So in your sentence, only Wir treffen uns fits, because it’s clearly an arranged meeting place.

Can I add the person we’re meeting, like Wir treffen uns mit Anna vor der Musikschule?

Yes, that’s very natural:

Wir treffen uns mit Anna vor der Musikschule. – We’re meeting with Anna in front of the music school.
Here uns shows that we are meeting each other, and mit Anna adds a third person who joins the meeting.
If you want to focus only on Anna as the object, you can also say:
Wir treffen Anna vor der Musikschule. – We’re meeting Anna in front of the music school.

Does vor der Musikschule describe place only, or can it also mean before the music school (in time)?

In this sentence, vor der Musikschule is clearly about place: in front of the music school.
For time, native speakers ordinarily use a bare time expression or vor with a time noun:

Wir treffen uns vor dem Unterricht. – We’re meeting before class.
Wir treffen uns vor acht Uhr. – We’re meeting before eight o’clock.
Using vor der Musikschule to mean before the music school (starts/opens) would be confusing; you’d normally say bevor die Musikschule beginnt / öffnet for that temporal meaning.

Where does the stress naturally fall in Wir treffen uns vor der Musikschule?

In normal, neutral speech, the main stress usually falls on the new or important information. If the place is what you’re emphasizing, it will sound like:

Wir treffen uns vor der Musikschule.
If you had already said where and you’re now emphasizing the action, the stress might fall on treffen or uns:
Wir treffen uns vor der Musikschule.
All the individual content words (treffen, Musikschule) get clear stress; wir, uns, and the article der are lighter.