those are good questions, and you came to the right place!
Glad you're asking ahead of time. It will take a little while for you to get up to speed.
Here are my first, minimalist answers:
1. Some do; either should work
2. Mine have been
3. Secure! Depends on duck size. Absolutely
4. Depends on breed
To expand a little - you might try the search option, as we have had many discussions on these topics. One nice feature is that if the topic posts don't cover something you'd like to know, you can post your question and that revives the topic. I have enjoyed seeing these things come up again from time to time.
Storey's Guide to Raising Ducks has helped many of us - see if you can get one.
Take a look into different breeds. There are small, medium and large. Calls are small, and often loud. Runners are a bit bigger (that's the breed I know), then there are Welsh Harlequins, Anconas, Pekins, Giant Pekins, Swedish, Cayuga . . . . . . So thinking about what your desires and abilities are will help. Do you want eggs? Pest control? Fertilizer? Pets? Peace and quiet (consider a hamster)?
Does mud offend you (consider a hamster)?
Do you want to raise ducklings? Start with adult birds? Are you willing to get extra females if the batch you get has too many drakes? How are you with medicating animals? Do you live near a duck vet (many of us don't, and need to do our own diagnostics and treatment, not to mention there's some expense)?
Take a look at the stickies - the treats list is fun, but the first aid kit list is educational.
Do you have a plan B if your situation changes? Dumping ducks is a heartbreaking and usually fatal thing.
Ducks have been such a wonderful addition to my life, and they have changed it dramatically. There have been some rough adjustments, but it's been worth it.
Do you like duck eggs? Have you priced feed? Do you already have a coop?
By the way, one rule of thumb for housing is 3 sf minimum per duck for overnight shelter, 10 sf per duck daytime if they have ready access to pasture, 25 sf if they have limited access to pasture (Storey's Guide, if I recall the numbers correctly).
Ducks need enough water to wash their heads in to avoid serious infections. They also appreciate enough water to bathe in. I use a concrete mixing pan, which I dump into a small channel that goes to the grape arbor. I have pea gravel around their water area.
My ducks are amazing sweethearts, I have eggs every day (4 - 9 from 9 runners).
I'll turn this loose and look forward to seeing others' responses.