K810i - NEED HELP UPGRADING FIRMWARE

Basically, I'm a handphone idiot and I need a lot of help with this.

I got a K810i from a friend about a month ago and you could say this is my first proper handphone... since my previous one was a really, really, old one about 5-6 years ago from Samsung. But I freaking love Sony Ericsson now.

Firstly, I decided that I should upgrade the software version (or if you call it, firmware...) because I think that latest versions have more features and stuff. And I also know that you can do it easily with Sony Ericsson Update Service. However, the more I Google and research about it, the more confused I am. There are so many terms and stuff that I read and do not know, also I've read that the latest K810i firmware brings with it problems. Therefore, I am considering upgrading or not.

Anyway, I don't have a need for Debranding, Unlocking and VKB patches, or anything else. I just need to be able to safely upgrade the firmware of my K810i version. My current software version is: CXC1250904 R6BC002 070607.

So, I need to know:
1) What does CXC1250904 is for? I know that R6BC002 is the software version, and I guess that 070607 is the date.
2) Also, what is the LATEST software version I can update to safely with SEUS, so that when I use my phone in the future, there are no errors or problems? Could you also tell me what new features come with the update?
3) I also would like to know if it is possible to flash my phone to another phone model? If yes, what is the best model I can flash to safely, so that when I use my phone in the future, there are no errors or problems?

Here's a thanks in advance to anybody who reads this :) Also, I hope someone can find some answers to my questions. Thanks a lot!