ground

Thanks for sharing! Awareness is a wish-fulfilling gem.

That may be called rebirth.

The ultimate guru is not a person, the ultimate guru it is the nature of your own mind. But as far as "does exist" or "does no exist" are concerned both do not apply. Thinking in terms of "does exist" and "does no exist" is the best way to never meet the ultimate guru.

I would put the question differently: "Which ancient Greek philosophers knew that they were enlightened?"

The concept of "development stages" is deeply engrained in ordinary worldly minds and that is why it is mostly taught this way. Otherwise the matter would hardly be accessible. So it is a skillful way of teaching. But all models of "development stages" offered by spiritual teachers are just models, i.e. possibilities. Individuals are too different and so are their individual stages. What certainly is important is focus and perseverance and patience. Some say that the basis must be faith others say that certainty based on rational analysis is more important than faith. Actually there are these two traits: bias towards faith and/or bias towards rational analysis. Different people different biases. Basically every spiritual journey can be summarized under three headings: view, path and fruition. One cultivates a view. One integrates this view with practices and finally the result/fruition will reveal itself. One can also speak of ground, path and result: The ground is already primordially present. The path serves to reveal that ground, not to create something new, and the result is the ground being fully and irreversibly manifest. So actually there is no difference between ground and result. And since the path arises from the ground and can only arise from the ground it is also not inherently different from the ground either. Having said that it turns out that if you practice you have already "attained" the result. If you don't practice you have in some sense already "attained" the result, too (because the ground is primordially present) but since there is no awareness of the ground if you do not practice delusions make themselves felt as if being independently real or true.

The question is how spiritual experiences differ from non-spiritual experiences and whether this difference is real or fabricated.

Provided "reality" = "ultimate mode of being (of phenomena)" and provided rationality is based on Arestotelian logic: Reality is neither rational, nor arational, nor both, nor neither. 1) Why not rational? Because nothing can withstand ultimate rational analysis, i.e. nothing can be found under rational analysis investigating into the ultimate mode of being although phenomena ceaselessly appear. This is a contradiction that cannot be rationally resolved. 2) Why not arational? Because without rational analysis reality cannot be fathomed/approached (although it cannot be grasped by rational analysis). 3) Why not both? Because of the law of contradiction. 4) Why not neither? Because of the law of excluded middle.

The sixth sense is fabricating continuously, that is why the number of senses may infinitely increase. ;-)

Initially the sphere of intuitions and conceptuality is the sphere of illusion, delusion and confusion, i.e. the sphere of collected conditionings and deeply engrained habits. Complete temporary cessation of intuition and conceptuality may occur when their nature, their conditions and effects, are seen clearly. There is no further realization beyond that and due to its transient nature it has to be cultivated through appropriate means.

Thoughts can indirectly affect matter, i.e. the appearance of matter, which is obvious in the sphere of science.

"Perception" is common parlance and as such it isn't an illusion but a conventional linguistic expression valid in certain contexts. In spiritual traditions the term "illusion" in the context of perception is applied for phenomena perceived since they are said to appear in a way which does not corrrespond to their ultimate mode of existence.

what qualifies a "master"?

your questions which appear strange in the context of conventional "every-day life" evoke the following question: what meaning does the expression "I know" have for you? i.e. when would you feel entitled to say "I know {this or that}"? what meaning do the expressions "exist" and "existence" have for? Asking "is it real?" evokes the question: what meaning do the expressions "real" and "reality" have for? The funny thing is that your questions are based on the hypotheses that "existence" and "reality" are more than mere baseless ideas. But how can you "know" ?

Calming the mind, being able to concentrate and think logically, experience the relativity of perception ... these are my ideas as to benefits.

Of course since every type of logic is a convention in the first place and if one does not agree to a convention of logic one cannot apply any logic at all. In some contexts however one will not be able to succeed at all if one does not apply a conventional logic, e.g. if one works in science.

The fact that "responsibility" is a thought before it is being expressed linguistically through speech or writing does not negate that it is an individual's decision to letting him-/herself being guided by the thought "my responsibility" or not. you can reject your responsibility or accept it. It is completely up to you, i.e. it is your decision, but from that you should not conclude that others will share or accept your view.

I'd suggest to look there for the start: https://en.wikipedia.org/wiki/Logic

There is a difference between being able to choose one's thoughts and letting oneself being guided by them. The latter lies in the sphere of an individual's responsibility