I really appreciate you taking the time to guide a complete stranger
No worries, if ever I can help then I'm more than happy to do so. We're all in this thing together.
I admire your willingness to question your experience and your honesty when describing it, you could just accept my suggestions at face value and go away thinking you've gotten stream-entry but you've got the integrity to question it and to publicly discuss it. That in itself is a skill which will stand you in good stead in future.
After have gotten up I had this "what the f... was that?" feeling, and I felt somewhat different - in an extremely good mood, peaceful and having and with sharper perception of reality. In my next meditations I got right into access concentration before even having counted five breaths.
That "what the fuck was that?" feeling followed by having "felt somewhat different" could very well have been 1st path. Again, this lines up with my experience of this but let me respond to your comments below:
The reason I write it off as being SE is that I could not get to any kind of cessation or bliss experience during the next five meditations the same day. I tried at least five different approaches, rolling back the eyes, trying to make the ajna center quiet, focusing on no-self, looking for the self, and seeing images of myself in my head. Instead, the vibrations of body parts and the brain seemed to increase in strength for each meditation after the possible A&P experience. My first meditation today was also quite noisy because vibration/shakings, but my last two meditations the sense of silence has again become predominant - a quit background where I watch vibrations come and go.
Due to the roundabout way I came to SE it's hard for me to be able to say what happens right after the path moment in terms of change in practice. I got SE before knowing anything about vipassana and only began serious practice a few months later so this is a bit of a gray area for me. What I can say though is that it took me a few weeks of sitting and posting a practice journal on here to finally be able to even identify a 'normal', as in not a path moment, fruition or any of the ñanas, and the same applies to willing a fruition to happen which is something it took me a long, long time to learn for some reason.
The method of rolling the eyes back does not always work for every yogi, it's a hit and miss approach for me but others swear by it. Personally, resolutions are what works for me so have a play around with that and see how it goes.
Your descriptions of a typical sit shows that you're getting into Equanimity at the very least so, just as I've said before, even if you're not there already then you're not a kick in the arse away from it. I recommend starting a practice journal, record the phenomenological details of your sit and it'll be easier to get a look at where you're at.
while I have strong concentration, the insight part of my meditation is too weak
Concentration leads to insight, insight leads to concentration.
I find it very difficult to note other than physical sensations and rather explicit thoughts, most often "planning thoughts"
Try noting in the way
Kenneth Folk describes here. This made a huge difference to my own practice.
Also I am afraid that I intellectualize anatta, rather than experiencing it. When I ask "what is it that is observing", I find it hard not to tell myself that "what is perceived as observing is merely a sensation". So this "what is observing?", is it like a koan or an attempt to see something? If so what is it I should expect to see, vibrations, images, or?
I know where you're coming from. Anatta is a simple fact, observable at any time and in any sensation - Nothing which can be perceived can be a permanent or seperate self, and since our entire experience is made up of objects coming into contact with the sense doors, the only way in which we can perceive the world in which we live, there is no self to be found anywhere.
My suggestion to you wasn't intended as a koan, I'm literally saying that you need to turn the attention towards the sense of there being an observer to experience this moment. All the time when you're noting, you're objectifying and labeling sensations in a systematic, clinical and precise way, as each object arises and passes away there is pattern of sensations implying that someone/thing is observing this. Investigate this.