The 90+2 doesn't really matter since she/he should not be depending on natural HP recovery in WoE. Spare points can go there, or STR. And yes, AGI affects Slow Grace to a large extent. But I really don't suggest you going a hybrid supportive build, because it isnt easy at all.
Support classes are always the hardest to play, and Clown/Gypsies are arguably up there. If you have to take up so many roles; Tarot, Scream, Slow Grace, AYS, Lady Luck, Sinx Song, Bragi, Apple, ANDDD POTSPAM, it's highly likely you will not be able to do any of them well enough. So my advice is to go a pure support build, most desirable would be a build which is suited towards dancing two of the dances that benefit your guild the most, and can backup as a Screamer. After soul link you might even be expected to juggle 4 songs.
As first choice screamer though, you are expected to scream ONLY. Get into the poem effect, and start spamming that hotkey. A screamer is most useful when he/she is able to stunlock low VIT enemies. Never let them have respite, even to tap ONE white slim. Remember, as a Screamer, always get out of your original party, and request your party leader to let you form another party with other screamers or a high VIT paladin to devote you guys. This is because you have a higher chance to inflict stun on your party members when screaming.
If I remember correctly it was (highest to lowest chance): Enemies>Party>Guildies