A lot varies depending on the keyword and how competitive it is really
How many keywords?
I tend to recommend less than ten to start with, maybe a couple more for geo targeting, if you are chasing highly competitive keywords then less so you can focus more on the important ones.
Keyword type..., small caps, caps? Comma spacing, "ABC, ABC" or "ABC,ABC"?
I always use lower case and leave a space after the comma, I don't think it makes any difference though.
Is important, there's no hard and fast rules for it though, you have to experiment, a non-competitive keyword won't need much density to do well, a highly competitive keyword such as "design" will need to get as dense as possible.
Extremely important, always has been, place your keywords as early as possible in the page title.
I don't think this matters much or maybe at all, it might even be part of the EMD update.
As in META tag? A lot of people say meta tags are ignored but I still take the time to do them well, it's just an opportunity to use keyword alternates from your page title eg "London web designer" to "web design company in London"