No, you can't still get Moderator or Inverse Moderator through normal gameplay, both were rewards for beating specific past events, and since those events have ended, buying or trading is the only way to get them now.

The difference between a Shiny unit and a Secret unit is that Shiny is a cosmetic rarity variant, while Secret is a separate, far rarer pull, with past drops showing odds as low as 0.01%.

Apex and Omega are enchant tiers applied on top of a unit using Gems, boosting its performance well beyond its base stats rather than changing which unit it is.

Yes, you keep the Units, Gamepasses, and Gems included with my purchase, exactly as shown in the listing.