You can always grind more

Seriously, even if your build is absolute trash, if you have big soul clarity you'll be so beefy that it won't matter. And grinding is not hard. You'll do it anyways!
So don't sweat it! The only caveat is that your cap for most of the game is 99 soul clarity. That is more than enough to handle the challenges the game throws at you until you can raise it, but there is a cap. Once you unlock 999 soul clarity, even the most horrid builds will be unstoppable by 200 soul clarity, and anything more is a flex.

Big tip: if you are grinding, play on hard and stockpile. Your stockpile multiplier is way higher on hard than normal, so even killing 2 enemies and stockpiling once will give ~5x XP for that first fight.

Again, not a guide.
If you want a premade build, there is a Gamefaqs walkthrough by a wiser man than I with a very good one, and there is no shame in using it means you'll get to the end of the game. I trust you can find it yourself. If you use his build, add an Aster Ashe transition for his supporter build IMO, but as is it'll carry you easily.

If not, important things:

0. You will probably want to trash your entire existing team when you get your transfers going. That's okay. Don't wait for higher level soul clarity starters, I'm in postgame and the largest I've seen is 5.
That's about level 50 on a fresh puppet, which you can level yourself in 15 minutes.

1. Never moon stance. It's not worth the HP hit. They really cranked up the number of enemies who splash your entire team so even your mages need every bit of HP they can get.

2. They nerfed the theater facets. You can still do the funny super AVD/CHR build from the first game, but it is a lot worse. Personally I wouldn't bother.

3. Always soul transfer at level 99. There is a wall that tells you to soul transfer whenever: don't believe it's lies. Every point of soul clarity EDIT *total level* increases the amount of XP required to level up, so you're just kicking the 99 can down the road *and* increasing the slope. EDIT apparently it doesn't make the slope too bad until total level 500, but the point stands. Also, unless you are intentionally sabotaging yourself on reincarnations your soul clarity and total level should be directly correlated. Again, general idea still stands.

4. Some personality choices do more than just stats. Some affect your luck. Weird and perverted do, at least.

5. Don't overthink it. Really, spending an hour grinding another round of 99s will do more than trying to spreadsheet a perfect build.

6. Not a build issue, but something the game didn't cover too well: the Parameter correction stat is actually a passive stat boost if that puppet is a supporter. IE, if you slot a puppet with SSS STR Parameter correction in a support slot, that coven's front line gets some % str boost (no idea what the actual numbers are).

Oh, how easy we had it in Refrain! Just pick 8!

Let me stress this again: you can make up for bad skills with more beef for the entire game. It might take a while, but that's what 8 hour long youtube video essays are for.

However, some details:
1. The skills for your starting facet will always have a 75% discount, even if you transfer to a new class. So, for a puppet that starts as a Shinomashira will always have their Shinomashira skills cheap, even on another facet.

2. The skills for your current facet and it's variant will be 66% cheaper. So for a Shinomashira, any Shinomashira or Shinobushi skills it has will be 66% off. You do need to actually have the skills first though, so if you transfer to one facet you will probably want to transfer to it's variant for the cheapo skills too.

3. Each facet has 2 innate skills. If you want to transfer those, you need to hit 99 before you can transfer them (never transfer before you hit 99!).

And in case this is frying your brain: All the above can be worked around with enough levels. Your favorite puppet had a bad starting facet for it's role? Just level more! More soul clarity = more skill points = more wiggleroom. Also the extra beef never hurts.

Now go finish the game! I personally walked away from it for a few months after unlocking soul transfer, but hopefully this guide helps people... not do that.