Learn English – Using Contractions and Conjunctions

I don't know if it is flat out "incorrect", but I do know many style manuals recommend against it.

When I was young, the rule used to be that you are supposed to use a comma between phrases (before the conjunction, not after) if there are more than two things so conjoined. If it is only two, the comma is optional. I'd usually leave it off. You'd only put a comma after the conjunction if there also happens to be a subjunctive clause inserted there.

I had an occasion to look at a more recent style guide, and I believe it said the comma before the conjunction is always optional. I don't have any guide with me right now, sadly.

You are right that for is a coordinating conjunction, the first of the so-called FANBOYS. But you cannot move a coordinated clause (starting with a FANBOY) to the front of a sentence:

I was hungry, so I ate.

*So I ate, I was hungry.

It is the same in German:

Ich habe gegessen, denn ich hatte Hunger.

*Denn ich Hunger hatte, habe ich gegessen.

However, you can move a clause with a subordinating conjunction to the front:

Because I was hungry, I ate.

Da ich Hunger hatte, habe ich gegessen.