Hello Charleston, to answer a few of your questions.
1. Not everyone is going to get the same "road signs" to the Astral. Some people experience intense vibrations, popping noises/white noise, cold spells, warm spells, while other people hardly experience anything at all. You will also notice that sometimes you notice that different times you will experience different things. This is why it is important to keep a log. So you can go back later and check your notes. Find out what works for you and what doesn't.
2. A Guide can appear to you in any form. He/she/it will normally take a form that is a. familiar to you, as of a deceased family/friend, or b. something that is not threatening to you, that will not create fear.Animals are reported quite a bit, especially bunnies/butterflies.
3. I have never experienced any does of don'ts on getting near another Astral entity. Possibly the reason is that in the Astral you are conscious energy and your energy might pass through another being. If this happened it would likely lead you to a fear scenario. Anything in the Astral that is counterproductive to further development is normally avoided.
I hope this answers a couple of questions for you, usually by answering questions here it will lead to even more, lol. Feel free to ask away.
Good Luck and Safe Travels