1. I'm pretty sure there is a limit but it's kind of ridiculous high. 150 pages or so, IIRC.
2. Password protection, not really. You can have members only pages, though. Similar but not quite the same. Members-only pages are available only to site visitors that have been approved to access those pages. You can also invite your contacts to create accounts once you've published.
3. GoCentral and WSB v7 are two completely different types of website builders, so there is no real comparison. I can say that if you want an up to date, modern website that's much easier to use and maintain and covers all the bases, GoCentral is pretty good.
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