What're the best low hanging fruit/charms as a whole in Solar Presence, Socialize, and Performances and are there any tripwires to avoid for mechanical reasons?
As has been mentioned, Harmonious Presence Meditation is one of the best entry-level Charms in the whole Solar set, full stop. It's very hard to go wrong with it.
As for Socialize, Mastery of Small Manners can either be completely irrelevant or absolutely invaluable, depending on how often diplomatic scenes come up in your game and how much your GM is a stickler for protocol. (My unfortunate experience is that the kind of person who runs the sort of game where Mastery of Small Manners' 'this Charm prevents you from committing any major faux pas' functionality would come in handy is also the sort of GM who looks at the Charm and says "I'm houseruling this to not have that functionality", but your mileage may vary.)
A better and more universally useful pick is Shadow Over Day. This Charm is often shat on in fan discussions, but being able to bump your Guile to superhuman levels for a pittance is actually very strong in the sort of scenes that tend to come up in games a lot (as opposed to white-room theorycrafting). More importantly, the Mute keyword lets you use this Charm in conjunction with the excellency to dump 6m into a beefy +4 enhancement to your Guile without flaring anima, which should reliably stand up to even superhuman scrutiny. Provided your base stats are good enough, for just one Charm, you get better than even odds at foiling the attempts of an optimized, max excellency'd Dragon-Blood to sniff out your intent/Intimacies, at no risk of revealing your Anathema status. Very overlooked Charm, but easily among the best as far as I'm concerned - especially if you're not planning to go for the full 5 dots of Socialize necessary to grab Guarded Thoughts Meditation, the upgrade that arguably obviates this pick.
Alternatively, for a more martially-inclined character who was so busy maxing out Wits that they had no points left to grab a decent Perception, Motive-Discerning Technique is excellent. It lets you roll read intentions with Wits, which can realistically be as much as a +3 dice difference,
and it grants double 9s - all for a measly 3m cost. The repurchase is also just super fun - you could make the argument that it's not as much of a high-value pick than the Charms mentioned thus far, but
it shapes play in an interesting way, and to me, that's pretty much the high watermark of a Charm worth purchasing.