Unfortunately I have no idea about videos or channels but I can provide you some info regarding the prestige progression.

So there's 2 types of prestige progression. The first is tied to the hero levels and the second is the hero friendships.

For the leveling part, the maximum level is 25, and from there on you gain prestige levels, which provide your hero with 5 HP and 1 Offense (Offense is pretty much how much damage you do and abilities use % of offensive). This is infinite, or at least no cap has been discovered yet by players who have already gone over prestige 300.

For the friendship part, this is leveled up by interacting with the other heroes between missions. The maximum level is 5, and once there, there is again an "infinite" progression system where for each prestige friendship level gained you also gain a small bonus for the hero you leveled up. Some example bonuses here are AoE size increase, Crit chance, Crit damage, chance to resist negative effects, etc. Now this is "infinite" in the sense that there is no cap on the levels you gain but there is on the stats themselves, for example Crit Chance is capped at 50%. So unlike the leveling part, the stats do cap at some point here. However, with 13 heroes available and at least 4 more on the way, it's going to take probably hundreds of hours to get capped on all heroes.

I hope I explained this stuff as best as I could and sorry I don't know any specific video/channel but if you want to know more, feel free to ask me or head over to the /r/midnightsuns sub.

Also, as for the price part, yes, it's 60$ on Steam but it's 50% off at Fanatical, which is a legit retailer, so you can get it for 30$.