the best thing you can do as a project if you want trans contributors to feel comfortable and safe...

Make it explicitly clear that you will not tolerate any sort of misgendering. Do not play the "centrist" who refuses to reprimand a contributor for repeatedly misgendering a trans contributor. it's not a "political disagreement" it's a basic sign of respect. Actually listen to trans people when they say things. Some forms of bigotry is not immediately obvious. I remember it was a night and day when I'd get in vc and people would immediately act uncomfortable around me and make side comments. They'd "slip up" in vc despite being used to calling me she/her and say "he" and then go "I mean she. I wouldn't want her to get offended". It's the snide comments, it's the shit that adds up. Listen to us, it's not just a case of "oh this person uses he pronouns for everyone by default" it's that after 3+ times of being corrected they continue making the same mistake going "sorry I forget that you're one of those".