I cannot recommend enough to cast Bless.

Bless is one of, if not the best defensive and offensive spell. It gets way better if you have party members making attack rolls.

Then as you approach level 12-20 saving throws become way more common, so the floating d4 on every save and attack roll becomes dead useful. I would even upcast this to cover you + the whole party. It seems like not a huge deal, but if you turn one weapon attack into a hit, and can save one party member from taking full damage from a spell, etc you have caused an extra ~10-30 damage, and protected your party from 10-30 damage (or from control spells!)

I’m also a big fan of Word of Recall, Death Ward, Holy Weapon, and Aura of Vitality.

Word of Recall can be very clutch. Especially if your party does not have a Wizard/Sorc with any fast travel spells.

Death Ward can protect squishies.

Holy Weapon can supercharge a fighter ( or monk of your DM let’s you cast this on their unarmed strikes). Definitely fun, and dead useful if someone else is already casting Bless.

Aura of Vitality is essentially ~70 HP you can dole out to your party. That’s basically a short rest at lower levels. I’d use this out of combat.

Doesn’t seem like it. Not sure if you ever got your answer, but this article says CR and D20 won’t be affected.

https://www.dicebreaker.com/topics/sag-aftra/news/critical-role-dimension-20-actual-play-sagaftra-strike-effect