Spårvagnen är tio minuter sen, så vi tar taxi istället.

Spårvagnen is the definite form: the tram/streetcar. Swedish often uses the definite form when talking about a specific, contextually known thing (e.g., the tram we’re waiting for).

• en spårvagn = a tram (any tram, new information)
• spårvagnen = the tram (a specific one)

spårvagn = tram / streetcar.
Pronunciation (roughly): SPOR-vang-nen (with Swedish å like the vowel in more for many speakers).
Also note the compound: spår = track, vagn = wagon/carriage → “track-car”.

In Swedish, sen is the common adjective meaning late (a delay).

• Spårvagnen är sen = The tram is late.
  sent is usually the neuter form of the adjective (ett sent tåg) or can function more like “late (in the day)” in some contexts. For vehicles being delayed, sen is the normal choice.

Swedish often states the amount of delay directly:

• är tio minuter sen = is ten minutes late
  No extra preposition is needed. It’s the same pattern as English “ten minutes late” (not “late by ten minutes” in the most neutral phrasing).

Yes. minut is a common noun with plural -er:

• en minut (one minute)
• två minuter (two minutes)
  The number phrase goes directly before the plural noun.

Here så means so / therefore, linking two clauses:
Spårvagnen är tio minuter sen, så vi tar taxi istället.
After så, Swedish still follows V2 word order in the new clause: the verb comes early. Since the subject vi comes first, the verb follows: vi tar.

Yes. If you start the clause with så, the verb must come before the subject (V2):

• Spårvagnen är tio minuter sen, så tar vi taxi istället.
  This is perfectly grammatical, just a slightly different rhythm/emphasis.

A comma before så is common and recommended when så introduces a result clause (similar to English “..., so ...”). In informal writing, some people might omit it, but the comma helps readability and is standard.

Swedish often uses no article in fixed “transport” expressions:

• ta taxi = take a taxi (as a mode of transport)
  You can also say ta en taxi, which is a bit more concrete/specific (a particular taxi / one taxi ride). Both are correct; ta taxi is very idiomatic.

istället = instead.
You may also see i stället (two words). Both occur; i stället is often recommended in more formal writing, but istället is very common. Placing it at the end is typical: ... taxi istället.

Swedish present tense commonly covers both “now” and “near future/just decided”:

• vi tar taxi istället can mean “we’re going to take a taxi instead” (decision made now).
  If you want to be extra explicit, you could say vi ska ta taxi istället (we’re going to take a taxi instead).

Yes: är försenad is also common and slightly more “official”:

• Spårvagnen är försenad = The tram is delayed.
  You can still add time: Spårvagnen är tio minuter försenad.