There are sites that let you ask your users questions, and building a mailing list can help you create your list of users.
I think you'll get much more bang for your buck if you talk directly to customers though. With a survey you can only ask the questions you know to ask. The more important questions? They are the ones you don't know yet that you need to ask. You'll find out about those from one-on-one conversations with potential users. Very little beats getting out of the office and talking with potential users face to face.
If you can't do individual user visits then going to a relevant conference and talking to people there can be similar - just be aware that lots of people there are rushed.
Regarding a SWOT how-to... a full thing would be a book, or blog post series, but some tips and URLs follow.
* Strengths and Weaknesses address internal factors.
* Opportunities and Threats address external factors.
* Strengths are things (tangible or intangible) that give you a competitive advantage (e.g., you have an existing business relationship with businesses in the tri-state area).
* Weaknesses are things that might hold you back, hinder your growth, or erode your strengths (e.g., not enough money, not enough technical talent).
* Opportunities are events representing positive shifts in your environment that you could take advantage of (e.g., new technologies, new markets), or areas where your competitors are weak.
* Threats are events representing negative shifts in your environment (e.g., commoditization, a big name like Google entering your niche), or areas where your competitors are strong.
* One technique you can use is to roleplay your competitors. What makes you as them be confident, and what makes you as them be afraid?
* Another technique is to segment your users into personas (fictional user characters that represent with their traits a segment of your user base) and for each use an Ishikawa (aka Fishbone) diagram to do a root cause analysis of what made them choose to buy. Also do the opposite to analyze what could make them pass on buying. See https://en.wikipedia.org/wiki/Ishikawa_diagram
http://articles.bplans.co.uk/marketing-a-business/how-to-per...
http://www.leadershipthoughts.com/how-to-use-a-swot-analysis...