The limitations on the comments is part of the structure of a Q&A website. It’s structurally different than a forum (like this) where discussions are threaded and you’re expected to read the full thread to extract the information. Why it’s short on Stack Exchange
The approach that I’ve seen work best is to make a best guess answer and comment to ask the original poster to update their question to add more information. After which you can update your answer to be more complete given the more complete question.
This has the significant benefit that someone who comes upon the question later does not need to pay attention to the comments. They can read the fully detailed question and then read the fully detailed answer, without needing to follow the whole thread back and forth gathering more information from the original poster.
This is why the Q&A sites are so popular compared to forums, because they’re optimized for the majority of users who end up browsing.
As a side note, I encourage you and everyone else out there to not worry about providing a “best” or “complete” answer on the first reply. The world is large and there is almost always others who might be able to provide a “better” answer, but if you can provide a helpful enough answer to get the person who is unblocked going forward that’s already a help. If you’re answer is exactly what people need it may be voted up and become the accepted one. If not it can still help others and provide an alternative view point.
In terms of completeness of the answer it’s often limited by the completeness of the question. Often questions are posed vaguely enough that answers are often just guesses. I recommend in that case being clear that the answer is speculation based on assumptions being made and I try to state those assumptions. On the hopes that if my assumptions are incorrect the original asker can update their question to add more details. And at that point my answer is to a different question and either someone else can provide an answer or I can update mine.