1. My fiance is my financial sponsor. He exceeds the income requirement by a good amount. Is evidence related to that all that is required?
Your fiance is your sponsor for all the requirements of the visa, not just the finances (there's no separate 'financial' sponsor - you can only have one sponsor for the visa: your fiance).
So, you have to provide the required evidence of his finances:
Assuming Category A (with current employer and earning more than £18,600 for at least 6 months):
- 6 months of original payslips showing a minimum pre-tax income of £1,550 per month
- 6 months of original bank statements showing the deposit of every payslip
- letter from his employer stating: current employment and salary, length of time with the company, length of time earning current salary, type of employment
- original job contract
- original P60
And you also have to provide accommodation evidence, and relationship evidence to meet the other requirements for the visa.
2. On that same note, since my fiance is my financial sponsor, do I as the applicant need to provide any financial evidence? From what I understand, I do not, but I want to make sure.
No, not unless you are meeting the financial requirement under a different category and are using your cash savings or non-employment income to supplement his income.
The online application will ask for your current employment details, but they are a formality. You can include a payslip and bank statement to show your income if you want, but it won't be relevant to the actual visa decision.
3. Do I need to provide copies of everything? It seems like that would be silly and only just double the number of pages (of which there is a good amount anyways...)!
Yes, you must send copies of every original document you want returned to you. If you don't include copies, they may keep your originals.
4. Also, I am a US National. Are my passports enough or do I need to send a birth certificate?
Birth certificates are not required. You just send your current US passport, and any expired passports you have (from all countries, if you hold more than one nationality).