I am hetero for the mthfr genetic mutation c677t. Everything I've read says I should be gluten/folic acid/dairy free. Advice regarding this mutation?

I can't agree. ~1 person in 4 is like you. The pathology community is divided over MTHFR testing. I'm undecided. A majority of people who take the test will be told they have an 'abnormal' result and are therefore in need of special supplements which they may then be offered by the folks who have done the test. Talk with your own physician and if necessary an authentic genetic counsellor. .
Not so extreme but.. This is common, affecting up to 50% of people,but the homozygous mutation is much more significant than hetero.Those with it have increased risk of depression, anxiety,cardiovascular disease etc. but it's just one of thousands of genes. My best advice is get a fasting homocysteine test; if 10 or higher take a multivit. with the L-5MTHF form of folate. See https://tinyurl.com/yacd86e4 and comment:
Spectracell lab. In tx has a test for this. Since you are pos. For it, you can visit their site for info or call them. Peace and good health.