Just popping in quickly, so please forgive the lack of personals.
PA80 - I found this to be a good start for MTHFR information generally (it should touch on some of your questions):
Most websites don't footnote their sources, so I've found this site very helpful for finding scientific articles:
Honestly, I wouldn't worry too much about it. Without any folate supplementation it's thought you have a two fold increase of having a child with down syndrome. Folic acid is extremely effective in decreasing this risk - I don't have any stats at hand. If you and DH are feeling unsure, I would suggest speaking with a genetic counsellor. I consulted with one before TTC through Mothersafe (NSW organization), it was extremely useful and bulk billed. Here is the website (has info for services in other states):
Hope this helps.
Hopeful - good luck today!
Elliemaysmama - I take 500mcg of B12 as it addresses some MTHFR issues (helps the body metabolize folic acid and lowers homocysteine levels). I'm not aware if it has any other functions that could help with auto immune issues.