All and any you can think of.
We had a discussion about types of energy here: Energy and Matter
Yes. Magick is change in energy directed by your intention.
Yes, the cosmos. This cosmic qi is an abundant and clean energy that you can never run out of and never become unbalanced by.
You can. But you’re already doing this naturally. It’s how humans work and stay alive. Every time you breathe in, eat, sleep, you pull in energy. If you are low other people naturally give you energy automatically. It’s our normal state to both give and receive in constant flow. Energy is always flowing, if it stops it is called "stagnant; and this causes sickness.
I would advise against making an entity to just randomly bring you energy without having a use for it. You cold get sick from too much as well as too little. Balance is necessary.
Again, the cosmos. Always the cosmos. Try this:
How to get energy from the earth and universe? - #7 by Mulberry
Learn to read and work with your energy body so you can balance it’s energy for health and power, know when to ground, that quality is important too, know when to cool off and when to warm up. Know thyself.