Wanted: Cantonese Materials For Foreigners Who Already Know Mandarin

I am not even close to committing to trying to think about beginning to learn Cantonese. It's Mandarin all the way for me (for now). But the fact is: I'm finishing my 3rd year in Cantonese Land (where I happily use Mandarin, by the way) and I really should at least know about the báihuà 白话 here. (Oh! The peer pressure!)According to this thread at Sinoglot, it'll be easier for me to learn Cantonese (if I ever decided to) by comparing it to the Mandarin that I already know than it would be for someone starting from scratch (seems obvious, but it's complicated, apparently). I won't be able to ignore the Mandarin I already know so I'll be comparing no matter what happens.What I'd really like to find is some materials that outline:

1) The different Romanization systems of Cantonese (and which one I should learn)

2) The tones (including how many there are: a shockingly difficult question for any of these native speakers to answer).

3) The phonemes

4) Anything else that would be helpful in getting the "discount" based on the Mandarin I already know.

I realize the target market for this resource is (can it be true?) even smaller than the target market for my own book, but I was wondering if these things exist anywhere (outside of the comments section of that thread, of course).Anyone (including you in that thread) have any ideas?