Cool. So, for this, a safer and way than dealing with the somewhat unpredictable human dead, and one that is popular in Western Occultism, is to get help and learning with the entities of the Ars Goetia. The Ars Goetia is a grimoire.
A powerful but also beginner friendly way to talk to those entities is called “pathworking”.
The book “Goetia Pathworking” by Corwin Hargrove is a very good resource for this. A few of us here use it including me, and have reported few issues and many successes.
Good call: I would not recommend any kind of covenant or pact with anyone at this time. Get to know them first and build a relationship, then you can talk about such things together. You don’t need a pact to get results.
Astral traveling, also called soul traveling, which is also experienced in Lucid reaming, Shamanic Journeying and Remote Viewing, is a skill of it’s own. Robert Bruce also has a good book on one way to do this as well:
https://www.amazon.com/Astral-Dynamics-Out-Body-Experiences/dp/1571746161/ref=sr_1_1?crid=J43KD810MYM6
Time travel can also be done using the astral travel techniques including remote viewing.
In my opinion, the spirit is already immortal, however, incarnating as human involved a amnesia that wipes out all memory of pervious experiences. So one form of immortality is non physical: you learn to regain and retain your memories between lives.
It’s not until the highest levels of self development into full ascension that you can combine and gain an immortal vessel. At this point your body is no longer fully physical, and you manifest a physical body to interact with the physical world on demand. This is very hard for higher beings on the other side, and part of being human is to learn how to reach this from being human upwards, and at the same time evocation by mages help higher beings to do this. It is the desire of many for the entities we talk to to be able to fully and independently manifest at will on Earth.
Note: at this stage, I have to say “in my opinion” because in esoteric matters like this, we can all have different “worldviews” or ideas about how the universe works. Different people have different philosophies and religious models of reality.
These are just mine which I made based on my own seeking. It’s a good idea to just keep reading and meditating and getting as much information as you can, then you can form your own conclusions. There is no “Truth” with a capital T, there’s just what works for you. 