Hi, in reply to the question about astral travel, I don't have lots of experience but I do have some.
I learned to access what I thought of at the time as "the jumping off point". Essentially this is a state, where one is physically asleep but spiritually awake. Getting to the jumping off point is something that could just happen to me when I lay down to sleep after a while, whereas actual "Astral Traveling", (what you do after you reach the jumping off point) is pretty hard.
Firstly, I will say that an empty stomach is a necessity. Don't eat the same day you intend to practice after noon if you plan to do the actual practice at night. I used to fast for a day or so to begin with.
You said that in your school they concentrate on the belly as a first step. I don't think it necessarily matters what concentration object you use but the belly is ideal as it isn't a small enough area to encourage the energy to rise too much and keeping the practitioner in the awake state. Essentially all I used to do was concentrate on the physical path of the breath, while lying down, get myself to a certain level of samadhi and then let myself fall asleep whilst maintaining samadhi. As long as you get it right you end up at the jumping off point, characterised by body-paralysis and sensory withdrawal (I guess it's Pratyahara but asleep? Idk) BUT with the spiritual body entirely awake. It can be confusing at first because it can seem like you have physical eyes and body but actually these are switched off and if you try to use them you can't.
Anyway, from here you can astral travel. To do that you need to be able to keep your level of concentrative absorption high and to be able to direct your energy body to move, which involves directing energy. If you can't concentrate you'll just end up lucid dreaming, normal dreaming, and/then/or asleep. I should stress this again. If you can't keep your concentration high, all the time you are in the Astral realm, you will just fall out of it and send up in a lower vibration experience. The higher the level of samadhi/concentrative absorption, the higher the level of interconnectedness with other beings, the more 'real' the experience becomes, the more interested and interesting encounters you are likely to have.
If you can't direct the energetic body, it really is a case of bumping into things for a while. I never got past this stage really, except on the odd occasion but I did learn to not try and use the physical senses to move around or sense the environment. Concentration becomes the eyes, intention becomes the feet. I'm just guessing that the chakras probably act as extra senses/limbs in this realm if you have opened and activated them.
It also requires equanimity to undertake this practice, something I found I did not have enough off. The experience of being in the astral reason can be strongly dysphoric for ill-prepared adventurers like myself. Definitely above my level then and now but would love to understand more.