I wouldn't worry about niacin - it and B2 are heavily required by the Kreb cycle to make ATP and you definitely need that. IMHO ideally you would want a small dose twice a day, like say 25mg twice a day (basically a low dose active B complex twice a day).
I would never take SAMe because if you are low in SAMe it is almost 100% because you are not recycling homocysteine properly (and so taking more SAMe is going to further raise homocysteine, a neurotoxin). You can get your homocysteine measured, a $60 test. Indeed SAMe levels are used asI a feedback to the methyl cycle so there can be value in taking SAMe just briefly to "prime the pump". IMHO no good would come from adding SAMe to a permanent protocol. To increase methylation, base nutrients are B complex, and TMG. If that is not enough, then support nutrients are needed like zinc,(&copper), magnesium, D3, anti-oxidants. Potassium is needed if you use active B's.
I am COMT +/+ and I can tolerate all the methyls I want. So...I do not believe the medical profession knows very much yet about how these genes work IN COMBINATION. I am also CBS +/+ and supposedly would have low homocysteine, yet when I started, mine was high. It is important to test. The genetic interpretations you are given do not apply to everyone