@ritter i had some bant lists posted earlier in this thread that are probably still just as relevant. going into a 4th or 5th color is good against combo decks, as thalia alone is not really enough. I ended up on judge's familiar and spell queller, but meddling mage (interesting!), revoker, bigger thalia (probably too slow/low impact), spirit of the lab (awkward), teeg (seems decent, doesn't stop tinker/mentor/vault), canonist (doesn't slow us down that much if you end chains with hollow one?), etc could also fill those slots.
I don't think you need too many off color moxen, and in general would want 2 spirit guides minimum, and 3 would be best imo. Turning extra creatures into discards/mana is very good. the interactions you mentioned are the main ones, but you can also EOT turn creatures into spirit guides to gear up for a bigger next turn, or power out a hate card turn 1, or beat down for 2 against control decks.
if you want cards against shops, the big idiots are pretty good - goyf, mandrills. not too many of the hatebears overlap, unfortunately. kataki is a card, but sort of fragile in the age of ballista.
the Gruw lists i ended up on were because i wanted more game against PO, and grudge certainly does help, but the matchup is still hard. I'm not sure you can stay Bant and still have a great matchup against PO. It always seems like you just die to a force of will into anything. Grudge at least will try to keep them low on resources and going too broken with outcome (in theory anyways...).
if i were to test more, i might try a 3rd squee and maybe meddling mage over something like Anger, even in a red list.
Anyways, congrats on the finishes and please let us know how things keep evolving!!