WCAG2 Implementation Comments

Hello,
I've been working towards updating my companies Web interface/content to be WCAG2 AA compliant, and potentially submit it as a Implementation.
A few questions that have come up while using the guidelines:
-are alt tags required?
-our site pulls aggregated content from an external source, despite the local content being WCAG compliant, our site at best can only receive a Statement of Partial conformance?
-for guideline 2.3.2, what constitutes a flash or flicker? Our site contains some JS behavior that causes a DOM node to slide across the screen at movement rate of 200ms (>3 updates per second) could this potentially cause a seizure?
-for guideline 3.3.4, our site contains mainly key words etc. and no legal or financial information, what does "Data" refer to in "Error Prevention (Legal, Financial, Data)"?
Regards
-peter