-Have not seen Sukujaka hit/knock anybody back on activation (then again i've never seen Yosuke whip it out point blank), so im also not sure if its safe to guard afterwards.
-For combos check the combo thread, and the General Discussion thread for Yosuke, I wanna say we had a bit of discussion on Yosuke in Sukujaka mode
-I dont believe the personae have their weaknesses in this game, that'd be a little unfair for alot of the cast due to Elizabeth having Garudyne,Agidyne and Bufudyne and the game sporting 3 lightning users (Kanji Narukami and Akihiko)
-As for combos canceling into new combos, most likely, especially since you can make all sorts of things possible with 1 more canceling and 1 more bursts. Again, refer to the combo and video threads for things like that.
Sorry if I didnt help much
Edit: Neurotic beat me to it with an actual helpful post :< Lol. Least he was actually helpful XD *thumbs up*