a) and b) are closest, but you need "would" rather than "will", as the sentences express a hypothetical. The speaker's subtext is that the intention is not to condone the actions.
a) and b) are then both good, and mean the same thing. It is entirely up to the speaker to decide which to use, although if it were me, form b) has more ...
Here "to" is not part of the infinitive, but a preposition. A preposition should be followed by either a noun or a pronoun (and a gerund can also be used as a noun).
That's why the structure of this sentence should be
I look forward to seeing you.
where "seeing" is a gerund.
No, that's not correct. "Tell" is a verb that serves as head of the VP "tell him", which in turns functions as a complement of "will".
"Tell" is in the form of bare infinitive, a form of verb that has no tense or aspect inflection and is not preceded by "to".
Thease are all grammatically correct, and seem quite natural to me. Any differences of meanign are quite subtle, and in practice I would regard them as interchangeable with mo difference of meaning at all.
All 3 are equivalent and correct.
before + pronoun + decide = before + deciding
Many (but not all) verbs simply mean the same between to V and V-ing. For example, "I like to eat" is the same as "I like eating".
wait ... before + V-ing = wait ... to + V
wait ... to V and wait ... before V-ing are simply verb phrases.