1. I think maybe I'm a deontological virtue ethicist. I guess...? Two things:
First, the most virtuous endeavor a person can do is to act in accordance with a categorical imperative - to act according to a necessary, rationally-derived, ethical rule. What exactly constitutes a categorical imperative is, again, not something I can prove deductively. However, I think that we can derive certain imperative rules from first principals (e.g. the importance of defending and maintaining free speech, which as per Hume, Popper, et al., derives from the recognition of our imperfect knowledge), which leads me to
Two, the pursuit of knowledge (or wisdom, or gnosis, or logos, or whatever you want to call it. Truth maybe?) is probably the highest good (beyond even pleasure), and possibly even an intrinsic good. I do like hedonism, and I think hedonism is as good a place as any to depart from when making general inquiries about ethics, but ultimately knowledge is more valuable than happiness (especially if, as the Greeks maintained, "true happiness" is only that which derives from wisdom). At the bare minimum, gnosis would be that which points us towards the imperatives against which we must act; without gnosis, we can have no ethics.
2. Hypocrisy. That is to say, wilfully going against ethical precepts you hold to be true, without either refuting or at least rejecting those precepts (at least, when you hold yourself to be a moral agent). Hypocrisy by way of ignorance is bad, too (e.g. the moral relativst who acts as a moral absolutist, simply because he's nto bright enough to see the contradiction), but deliberate hypocrisy on the part of people who do know better is worse.
I don't know if I'd say that's "sinful", necessarily, since that word carries certain religious connotations I don't adhere to. But I don't know if there's a better word (I've got problems with "problematic" and I think "toxic" is ironically more toxic than "sinful" is) so let's just stick with sinful!
3. Not as much as I should! I'm in the habit of playing Devil's Advocate, so in those cases where I'm called upon to, say, make an argument, or defend a position, I think I usually tend to examine "my" position, which often involves some sort of ethical dimension. However, as I'm getting older (and thus more confident in my ways), and I'm spending more time isolated in my dingy seaside house (shitposting online), I think the frequency with which I examine the morality of my actions has slipped. Maybe a couple times a week? Possibly more, but probably less.
4. a. and b. God, I don't know. That's a really broad question, don't you think? It's like, HEY, Snek? Why don't you just sum up a lifetime of epistemology in a Kiwifarms thread?
I mean, clearly, it's both, right? I've been influenced by authorities, AND I'd run through my own process of reasoning. Now, that process of reasoning was itself influenced by authorities, who maybe encouraged me to reason on my own - but my decision to read and accept the arguments of these authorities in the first place was done under my own initiative.
I don't know. It's one of these chicken-or-egg, Free Will versus Determinism kind of things, right? This may be vanity, but I'd like to say it was mostly me (or at least, me doing the choosing between all the influences and arguments I've heard), but if it's true that my ethics can be derived from logically-consistent principles, then I guess the ultimate authority here would be "logic", or "reality". "Reason" maybe (although I actually think I prefer empiricism to reason).
As for human authorities? Probably things like my parents, teachers I've had, authors I really liked. Also some negative authorities, too: authorities who rubbed me the wrong way, and got me primed to DISAGREE with them, such as that one teacher who yelled at me in fifth grade for playing soldier at recess, even though she'd just lectured us about the evils of the Second Amendment. ngl, I am not above holding petty grudges, although I'd like to think that it all eventually evens out thanks to sound epistemological methodology (I've had people I LIKE that I nevertheless wind up disagreeing with later, such as Dawkins and, horribly, Stephen Jay Gould)
5. Possibly the moment I realized I was an anarcho-libertarian? I've always really been like that, but being raised in a society like mine, I always just assumed I was progressive by default; realizing I wasn't, and that was OK, was a great weight off my shoulders. Freed me from a lot of second-guessing and fears of social unacceptability - so, while it's kind of a SMALL thing when measured against everything else in my life, it's at least one of the watershed moments that helped me come to terms with my aims and responsibilities as a moral agent.