Apologies in advance, as I'm 100% sure the answers to these questions will be covered in other threads. I just noticed the NTP challenges in this forum, which I'm keen to try out asap. But I'm just hoping to get a few basics sorted at the moment, before the weekend. I also apologise in advance for any incorrect terminology.

For the record, I am using a Canon 40D with a 18-200mm Canon Lens. Now:

1. When taking landscape photos, usually in the wee hours of the morning before and up until sunrise, in the Av mode I am setting the aperture to f22 (the highest it will go). I do this to hopefully capture as much detail in every corner of the image and get what I hope is the best DOF. However, I have noticed a lot of similar (though obviously far superior) images on this forum are taken at f16.

Can I just ask the benefit of using f16 instead of f22 in a moderately low light landscape photo? Is it that the f16 allows for a quicker shutter speed and therefore less movement? And the f22 allows for a longer shutter speed and more chance of movement?

2. For my Canon 40D, is there a way to set the shutter speed in Av mode? Or alternatively, a way to set the aperture in Tv mode? At ISO 100 in each mode, I find it very easy to white out a photo setting a long shutter speed in Tv mode, but I can't see how to manually set the shutter speed in Av mode. I assume it's auto in this mode?

Aside from using the Manual Mode (I assume), I was just curious to know if there is a method using Auto Focus to set both the Aperture and Shutter Speed?

3. I have also been playing around home with the Aperture. Taking photos outside in the full sunshine of my pups and beer bottles (a new assignment I have set myself - humerous, to me at least). The problem I am constantly getting, setting a really low f number, like, for example, f4 or even f8... the images are turning out soooo dark. Even in full sunshine. I started out with the low ISO to keep the images sharp and noise free, then I went up to 400. But they kept coming out dark. Do I need to increase ISO to over 1000, but then will it bring too much noise and unsharpness to my photos? I ended up setting the ISO to Auto, but they were still coming out dark when I had it on a really low Aperture setting. Is there something really simple I'm missing?

4. Easy one. I see a lot of you guys taking shots with super long shutter speeds... as in minutes even. The longest shutter speed I can get on my camera, that I know of, is 30 seconds. How on earth do you get a longer shutter speed than 30 seconds using the Canon 40D?

Sorry again, guys, these are probably all really stupid questions. But any help would be most appreciated. Thanks.