well it's all in the "abstract" part, so obviously you don't want to just take a picture face on an entire building. The one's that I see and like the best take a portion of a large building, not the entire thing. which you may or may not have already noticed yourself, just saying words over here, lol.
Flikr user 'vulture labs' has a lot of great architecture shots in London. You might look through his gallery.
As Shakurai-Stock mentioned wide-angle lenses are generally most useful but often have distortion issues and there are often perspective issues to deal with. Software like PTLens can be very useful in these cases.
2. Yep, mostly wide-angle lenses. Just be aware of potential issues with chromatic aberration and pincushion/barrel distortion. You may need to do some post work on shots with lots of parallel lines. Alternatively, a regular 50mm lens might work in some cases, and be less likely to give you extremes of chromatic aberration or distortion.
3. Never been there, but you could do a search through google or flickr to see what turns up. You might be better off just wandering around on your own with no particular destination in mind. If nothing else, try to resist the urge to photograph some place that’s already been photographed a billion times already, unless you know you can show it in a way that is utterly unique.
number 3 sounds about right. While I do some post on images I've already posted on here or tumblr, I want to keep these upcoming shots a bit less photoshopped and more as they were (colourgrading or light touching notwithstanding). We'll see though.