1) This might be a stupid question, but what if your sens is too high and can't locate the angle? If you were to lower your sens, it would probably be hard to pogo comfortably(if you have to) after the bhop.
Scorch covered this quite well, but to add to what he said, generally angled bhops are used to skip very long downpogos, and while I agree it isn't always practical, you could even switch back and forth in console between your sensitivities after you shoot if you type in a really low value and your actual sensitivity, and then accessing them using the arrow keys (up and down) and still have enough time to perform the bhop.
Of course the method Scorch suggested is a lot better for every situation.
2) Do tts, course wrs, bonus wrs, and maybe even normal map runs(whereas the demos are not uploaded) with use of pitchdown get wiped too?
Yes, they will all be wiped. Even though there is no time saved by using pitchdown (besides time spent grinding) if you are inside of the starting zone of a bonus for example, it will still be treated with the same mindset of one done during a run.
3) Are there any 1st-chance warnings before the wipe/ban offense?
If kurt.santagada2003 decides to try pitchdown on a single run without knowing the consequences, then some leniency will be shown regarding a total wipe or ban, but the offending time will be wiped regardless and the player will be warned. However, if the player continues to use pitchdown, they will face the punishment as defined in the rules. With that being said, the punishment is not concrete, and could become more or less severe depending on the context.