Foils are a good idea the die doesn't touch ypur scalp so you're less likely to absorb any chemicals. I waited til 12 weeks to be safe...
Yup either plant based dyes (my dr recommended) or since a lot of salons (atleast by me) don't carry it they will usually have an oil based dye thats ammonia free :) I'm having my cousin dye mine at her salon in 2 weeks she said that is a good alternative to plant based dyes :)
I would wait until you hit your second trimester. Also, when you do it, try to get something without the ammonia and NO bleach. I used the new Olia that is oil based. There's no smell and it works great.