Ok here’s how it works.
1st, forget Chronox. Hes a terrible monster.
2nd, monsters hatched from eggs go in rarity from Epic, Super Epic, Legend, and Mythic.
3rd, Epic mons require Epic potions, Super Epic mons require Super Epic potions, and so on and so forth.
The exception to this general rule is monsters you get from Monster Hunt (the first 4, Kong, Raptor, Galv, Wolf), Chronox who, as mentioned earlier is bad, and monsters you catch offline on the islands and in temples.
The monsters you catch in the temples that have 3 stars but the ability to become 5 stars can receive Epic potions as long as they are not Ultra Evolved into their 5 star forms, as 5 Stars means Super Epic and Super Epics, as stated above, require Super epic potions. The 4 starter mons are the same. You can ultra evolve them to their 4 star forms and they can use Epic potions. Once you Ultra Evolve them a second time into their 5 star/Super Epic forms, they will require Super Epic potions.
The maximum amount of potions on any monster is 9. The potions apply a benefit to your monsters at 3 different levels, +3 (meaning it has been given 3 potions), +6, and +9. Each of these tiers apply the following 2 effects: an Increase to the Entrance Speed (the amount of seconds your monster enters the field with before it can move) and Move TU (the amount of seconds required to use each of its skills.) Having a higher amount of potions on a mon makes it faster and able to make moves quicker in battle, thus making it more effective.
To wrap this all up, as Epic potions are FAR easier to come by, especially in the beginning of the game, than Super Epic potions are, you are better off using Epic potions on you 4 starters and island caught mons that can Ultra Evolve rather than evolving them first and having to use the far more rare Super Epic potions.
Make sense?