I highly advise staying away from AI. I find them detrimental to my skill in any fighting game I play, for some rather fundamental reasons. Computer opponents, especially in Hisoutensoku, never think - they only react. This works against you in two ways. Firstly, they react, but they do so faster than any human could. Thus, they can't ever be "mindgamed" unless whatever you're doing is a frametrap/punisher, or they're somehow programmed to not react to something (like not blocking the last hit in a Dial-A-Combo as mentioned above). Secondly, because they never think, they never learn why they're getting hit or even how to mix up their moves, and they become incredibly predictable. This sounds good on paper if your goal was to beat the AI, but it makes you develop bad habits that will almost never work against a human. When it comes to learning how to fight humans, there really is nothing like the real thing. Oh, and as for improving tech skill with combos/blockstrings/etc., that's what Practice Mode is for.
I know this deals more with technical aspects than direct strategy, but I've been wondering about the availability of frame data for characters. The Hisoutensoku Wiki only gives frame data for a little over half the cast, but even those for the ones that do aren't complete (I don't think anyone has frame data for skills and Spellcards, for instance). Googling didn't help, and I don't have to equipment to analyze this kind of stuff myself.