As far as support - this seems to be an area that is up to the Consulate Officer's discretion. I mean, I had almost nothing of my own, and Phil had a bit in the bank, but nothing impressive, and they hardly gave it a look. And he was going to have to support four of us - himself, me, and my two sons!
I would send any and all correspondence you have showing "validation" of the relationship, especially as you are not going in person. Send copies of photographs of the two of you together, if possible.
The actual "letter of support" comes from your fiancee and should state that she is able to support you without relying on public funds until the marriage and you get your FLR and are eligible to work. It sounds hokey, but it's necessary. If you're going to be living at her place, then copies of her mortgage/lease/permission from landlord for you to reside there are absolutely necessary. If you're staying with someone else (say, family) you need their mortgage/lease/permission from landlord - and it helps to show proof that you're looking for your own accommodations.
When in doubt, send MORE than you think you should send. Keep copies of EVERYTHING. Remember you have to send your fiancee's passport as well as your own. And make double sure all the forms are signed properly. I went in person so I was able to ask questions when I got there about whatever confused me. But mailing off means you don't have that luxury. :-/
Visit
www.come2uk.com and see if it might be any help. I keep plugging this site, but for just asking questions it's pretty good. The forum is very much more "functionary" than "supportive," so you'll have to stay here for charm and hospitality!!
Keep us informed - and take it easy. Everything will go just as it's supposed to.