I can't help on the mtx, I've never taken it.
I can tell you what I did before I got pregnant (I have a four month old). I was lucky enough to be in remission, but I had to adjust my meds. Talked to my GI and PCP first. GI did some blood work while I was still on all meds. Things looked good, so I went off the meds I needed to and we did some more labs to make sure things were still alright. They were and he gave me the go ahead. I was already on prenatal vits, but I added a DHA supp to.
Good luck! I really miss being pregnant. I felt great the whole time. I am in a mini-flare now, my first in almost five years.
Hoping to stay in remission after the birth of a healthy baby girl. On Pentasa during my pregnancy, went med-free 2 months to nurse (stupid), but back on Pentasa and still nursing.