Close, EI, but not quite.
I remember a topic from the GameFaqs message boards a fair while back which explained (VERY in depth) how every aspect of the Style system worked.
Basically, you get your first style from the very next battle that occours. Every style after that is awarded after going through ~255 battles, I think. I KNOW it's more than 200, though. The number of battle needed to upgrade a style varies depending on which Type it is. I think the range is Shield-100 battles, Guts-120 Battles, Cust-140 Battles, Navi/Team-160 battles, and Hub-180 (I don't know, actually, does Hub style even GET upgrades? I can't remember that...)
All style elements are chosen completly randomnly. Despite what anyone might say to other effects. I can vouch for this, as my first style was WoodShield, despite the fact that I had never even OWNED a single Wood type chip before obtaining the style, and that, in terms of elemental chips, I used Fire type almost exclusivly. The unfortunate part of this is, the element for the next style is selected right after you obtain another, so you can't just reset one battle away from a new style to get a different element. Bah. It took me FOREVER to get HeatCust...
The Style Type, however, is not random. It is determined by the method you attack enemies and by the chips you use. Any non-Navi attack chips (With actual Damage numbers, not like LavaPanl or MetShield's reflection) will go towards giving you a "Cust" style. Note that selecting multiple chips at once gives a slight extra boost, and using P.A.'s adds a HUGE boost to the Cust style.
Any other Non-Navi chips go towards Shield. It's that simple.
Using the Buster to defeat enemies or to just damage them adds to Guts. Using fully charged shots to defeat enemies adds a good deal.
Using Navi chips adds to Team/Navi. It's best to try selecting one plain Navi chip at a time for this, or you'll add too much to Cust. and get that instead.
I THINK that's everything...
:sweat: I should go to bed soon... my spelling has gone completely horrible... :sweat: Ah, so has my grammar skills...