Is this the correct way to make a direct quotation in the future tense? "..." a déarfaidh sé.
What about in the present tense? "..." a deir sé.
What if you want to put the quotation at the front of the sentence like this? Dúirt sé, "..."

Go raibh maith agaibh.

Basically, yes. I would spell it adeir, adéarfaidh, aduairt, because the "a" is not a relative pronoun, but originally part of the verb, but, yes, in Standardised Irish, they do spell it separately. These forms are used when the "said he" clause comes after the thing said.

Yes.
BTW: "..." a deir sé is often used generally in past tense as a quotation marker in story-telling in Connacht (instead of a dúirt sé).

In front of the sentence:
Dúirt sé, "..." (He said: "...")
or:
Is é a dúirt sé (ná) "..." (What he said, was, "...")
Dúirt sé mar seo, "..." ("Thus he said, "..."), rather rare

I don't think this is just a Connacht trait. I would generally understand/expect a deir sé to imply the past tense in much the same way as "says he" typically does in English. That is, of course, unless it was particularly clear from context that this is intended to be interpreted as a habitual action in the present.