I'm clueless on (yet amazed by) advanced photography, so I hear you! :)
As far as I know, your photos will be more secure with Flash. Flash will run in a browser, of course, but it's self-contained, so your images are tucked away in the Flash file, so to speak. Of course, if someone is extremely persistent, they could hack into the Flash itself, using various utilities or Adobe Flash development tools to get at the photos. A Flash person could give you the most up-to-date thoughts on this, but I think this is pretty much true. Would this happen? Probably not enough to worry about at all.
Nowadays protecting intellectual property is tricky.
Squarespace looks pretty interesting... I've never seen it before. Funny, their CTO has a re-spelled version of my name. :) Features and pricing look very good, especially given that they're in a very expensive neighborhood (Soho in New York). Importing from WordPress, Typepad, and Moveable Type... sounds impressive.
Sometimes it's worth having a hosted system if you're not super-techie, as they take care of (and most importantly, are on the hook for) updates, installs, and keeping everything working, and depending on the firm, they might (and I say might) be quick and helpful with your tech support questions.
You could try something I often do with companies I've never seen before - I just send them a random question about their stuff, and see what they say. This gives me a sense of whether they care enough to answer emails, and gives a sample of their customer service skills, communication ability, and so on.