A lot of this can be easily found on the internet, but I'll answer the rest
http://en.wikipedia.org/wiki/Veterinary_specialties (list of specialties - although the mention that specialists get paid 2-3 times a GP is incorrect - even twice is pushing it. And the mention of a starting salary of a vet specialist is 140k, with average of 150 to 350k, is absolutely ludicrous. I only
wish I could get paid that much after I finish).
http://www.acvo.com/ (Veterinary Opthalmology)
At least 50% of veterinarians, especially those graduating in the last couple years, do one or multiple internships after they graduate. I think about 10-15% go on to become board certified in something via residency.
Whether a residency is "worth it" or not depends completely on what you want to do. If you want to be a general practioner, you don't need one (although I know many who do Internal Medicine internships and/or residencies). If you feel a calling to a specialty, then do it.
The veterinary opthalmologists I know seem to love their job. I can't quote exact salary numbers, but it's in the area of pathology and radiology and other top specialties (i.e. you max out at around 90-140k after 10-20 years depending on whether you are in an academic referral hospital or a private clinic) and the lifestyle is pretty relaxed. Most of them also do all their own surgeries. Most of the emergencies you're going to see are traumatic, usually requiring extraction.
However, the number of optho residencies is quite low, and you'd likely have to do a 1-2 year rotating med/surg internship before even applying.