Amazing Cultivation Simulator Guide

You've probably been told not to start with a Yaoguai and you probably decided to heed that advice after, at most, the first or second time you made the mistake. The important thing to know about Shapeshifter Tribulations is that you have to manually activate them. Select your Yaoguai, hit the yin-yang symbol on the right and then click the icon that tells you how many days until your next tribulation. I didn't think it looked clickable but it certainly is! You then select a spot to have your fistfight with Heaven.
Yaoguai that have successfully survived their Shapeshifter Tribulation will never have to undergo another Shapeshifter Tribulation (but may need to survive a different Tribulation based on how you choose to progress their Cultivation.) You can use a drop-down menu that appears in the bottom left to switch them between their beast, monster, and human forms. There's statistical differences but I'm unsure what specifically they are.
I couldn't tell you what else applies.
Spirit Soul Gems are a ♥♥♥ to farm so buy them any chance you get because you're unlikely to have access to them when you need them most. There is no consistent farming method to get them, unlike Anguish Soul Gems (Hell Gates).
Don't make a bunch of storage, you'll get a miniature universe relatively early on.
In order to construct the miniature universe, all you need is a cultivator at or above Golden Core. Examine the orb, then examine the scroll, it's in the building category "Wonders". It requires some rare-ish resources but it's not terrible. (Fire and Ice Essence, Holy Stone Blocks, etc.) The small offshoot pillars of the mini-universe are not necessary - all they do for you is let you take items from the universe out at the location of the pillar instead of the universe, but most things your disciples will have teleported to them.
In light of this and other reasons, there's huge advantages to having exactly one inner disciple who blitzes through and gets a garbage golden core. Primordial Spirit (the tier after Golden Core) takes a long time to reach no matter what you do, and it's worth rushing to so you can unlock the spells that boost allies' stats by a percentage based on how low the stats are at the time you cast the spells (there's one for Perception, Constitution, Charisma and Intelligence. None for Luck or Potential that I'm aware of.)