Here's part of an explanation found here:
TO ... is used in cases where a "transfer" happens.
E.g.
- I will give this book to you. (from me to you)
- I will go to work. (from home to work)
- I will talk to her. (information goes from me to
her)
FOR is used in the following situations:
for the benefit of
e.g. I will do that for you.
purpose
e.g. This brush is for painting.
Not exactly a rule, but in general to applies if the word coming afterwards is specific.
For is used if the situation is more abstract.
For this reason, both of your examples for alms make sense depending on the context.
We give alms to the poor. (Which poor? The beggars downtown. We give alms to those beggars.)
We give alms for the poor. (Which poor? I'm not sure. Our charity determines who receives the alms.)
For real indeed has a kind of slangy/childish connotation, which I'm sure is why it was used in the title of that movie (a quick Google search reveals that the film is about a four-year-old who has a near-death experience).
However, it also does not mean the same thing as real: if something is real, it exists, while if something is for real, it is legitimate.
Merriam-Webster backs up this adjectival sense of for real (definition 3.2 and 3.3 at that link):
2: genuine "couldn't believe the threats were for real"
3: genuinely good or capable of success "not yet sure if this team is for real"
To be fair, that dictionary also gives genuine as one definition of just plain "real", but I do think that "for real" is much more about legitimacy than "real", to the point that there is a definite difference in meaning. Consider the following examples (mine, this time):
A: I don't think this pizza is real.
B: I don't think this pizza is for real.
If I were looking at a plastic replica of a pizza, I could say A but not B. In contrast, if I had just been given a pizza that I was told was from a famous restaurant, but in fact looked very unappetizing, I could say B but not A.
Of course I contrived that example to demonstrate the difference in meaning. To return to your original question, Heaven is real and Heaven is for real do indeed mean pretty much the same thing. But my point was to show that real and for real are not always interchangeable.
As for the grammar part of your question, I don't think for real is grammatically remarkable - there are other structures of the form "[Noun] is for [adjective]", e.g. This coffee is for free.
Best Answer
I believe that your usage is correct. For clarity, you could add the words that are assumed in your example, i.e.
You could also use "before" in its causal sense, i.e.
Not a grammarian, just like writing. Cheers.