Hi BBuck,
I think I can help out in this area;
- is it a good thing for SEO?
A Q&A section can absolutely be beneficial to SEO. Any value-added content to relevant topics is great to include in your website and User Generated Content (UGC) is a goal of many successful SEO strategies.
- Or a potential pitfall for SEO?
It's a pitfall if it is not value-added (spammy) or negative to your business objectives.
- If it is used often and users post relevant topics related to the website content, will it help the overall DA and websites SERP performance?
Consistency is a common trait of successful campaigns and value-added, topic related content has a high impact on domain authority (DA) and search engine ranking position (SERP) performance. It can only help you achieve your goals when used properly.
- Are there inherent risks for website security when using a Q&A?
That would depend on your own unique website environment (server host, plugins, ect) and I would encourage you to have consistent communication with your hosting provider and website manager.
Make sure to continue to screen UGC for spam related content, non-value added content, and other innapropriate content.
- Are there any other questions I should be asking?
Yeah, most of the time
Here are a few to keep you thinking...
Are you making it easy for your users to ask questions?
Are you making it easy for those responsible to answer questions?
Should you require a login/purchase/information to post questions?
Where should you show the questions? (from a UI perspective, has more impact for ecommerce companies)
Best of luck!