Since andselisk answered the other question, let me take this one.
Since this is in general a question about SE's expectations of moderators, I'll preface this with a link to the moderator agreement: https://chemistry.stackexchange.com/legal/moderator-agreement Every mod needs to sign this, but in theory there are no requirements beyond this. You might find that this actually answers quite a few of your questions.
What is the workload? How regularly do you feel needed on the site, of that time how often are you available, and how often are you actually on the site (do you work more or less than required)?
There are two questions here, one about the frequency of visiting the site, and one about the total amount of time spent on the site.
Re. frequency: I pop in quite regularly, i.e. every few hours, and virtually every day (you can see this for yourself: on my user profile there is a part which says "visited X days, Y consecutive". Click on it and you will see which days I have opened the site.) This is pretty useful as it lets me get to stuff that needs to be handled, e.g. very rude arguments, trolls, spam etc.; and it also lets me respond to requests from other mods for help or advice. In practice, I don't think each individual mod needs to be here too frequently. Rather, it's more important that one of the mods is around frequently: that is, the workload of checking in frequently can be shared.
Re. amount: even though it has decreased, I tend to spend quite a bit of time here—anywhere between several minutes and several hours per day. One must differentiate, however, between the things that I do as a user (writing answers, editing posts) and things that I do as a mod. In terms of the actual moderator duties, there is honestly very little to do, especially after dividing it across the team. Most flags don't even have to be handled by the mods, as the community can take care of them. The most time-consuming thing is almost certainly meta.
What are demands that have explicitly been set by SE management (if any demands have been set) on how much time you should devote?
There are none, see the moderator agreement. In fact, one can do almost nothing for a long period of time and still remain a moderator. This was the case with ManishEarth, for example, who got busy in real life and visited very rarely.
Does becoming a moderator require that you reveal your identity to SE admins? (changes in privacy?)
No (see mod agreement). My real-life identity can be found via my profile, but that is my own choice. For example, andselisk is completely anonymous.
Do you have any concerns regarding interaction with the SE admins?
We (the current mods) nearly never interact with SE (the company) or its employees in any substantial manner. So I'd personally say no.
You can choose how much you want to participate on Meta.SE, as well as the SE chat community. Personally, I don't like doing that, so I do virtually none of that, and I see no compelling reason to change that.
I'm aware of the whole SE drama that occurred a while ago, and although I certainly didn't like certain aspects of it, I never really contemplated quitting over it. I have never viewed myself as being subservient to SE, so I don't have any scruples about "working for an evil employer". I am not part of SE-the-company, nor do I dictate their actions, so I can hardly be expected to feel that staying as a mod makes me complicit in their behaviour. In fact, I chose to be a mod in order to benefit the Chemistry site itself, and I felt like quitting would have been a dereliction of responsibility towards the site and its users.
Obviously, there are strong views on this. But I did what I thought best.
There is some secrecy regarding tools available to moderators (possibly above and beyond those available to members with the highest rep), which for instance allow you to track the behavior of users on the site. Users are asked to avoid asking for information about this (link not found but there is a page where this is stated in a particular context). Should we be worried or not?
I don't like the secrecy that surrounds this, because it engenders suspicion and ultimately resentment. So, I'll tell you that yes; mods can see a fair bit of info. This includes the name and email you sign up with (nothing stops you from using fake ones), as well as IP addresses, as well as times of logging in. It's nowhere near as much info as SE-the-company has on you: for example, we can't see which posts you voted on.
All of this info is hidden behind a couple of buttons, and any time we view it, a permanent log is made. Part of the moderator agreement is to only use this info to carry out mod duties (e.g. investigating improper voting). Thus we are bound in some sense to use this carefully.
Beyond that, however, you do need to rely on some kind of trust. A rogue moderator could harvest data and sell it off, for example. I can promise that I have never done anything of the sort, nor do I intend to :-) However, if you really want to be "safe" on SE, you should take similar steps to those you might use elsewhere: for example, don't use your real name or real emails, and use a VPN or similar to hide your IP.
Are you (or were you) legally subject to some sort of contract (for instance an NDA)?
Well, there is the agreement; but beyond that, there's nothing but "customs" and "conventions" which stop us from blabbering.
If you do not comment about some aspect of moderation, is it because you are legally subject to some sort of contract (for instance an NDA)?
Traditionally SE has been reluctant to tell users about what info moderators have access to. Part of the reason is supposedly to avoid people figuring out how to circumvent them. But I think this approach is a bit shady, and also increasingly untenable. All of the info can be found amongst a bunch of scattered posts on Meta.SE, and so my answer to Q4 broadly describes what's available anyway.
There's another thing we refuse to comment on, namely suspensions. We don't answer questions about "why was user ABC suspended", or if we do, we keep it extremely vague. The reason for this is far simpler: there's no point doing so. Suspensions aren't meant to be a public shaming, and indeed, once a user is unsuspended there is no more public indicator showing that they have been suspended before.