Here you go, since you can't say anything except your repetitive strategic overview of the balance of forces on this - some straightforward yes/no questions;
Am I a terf because I think any group promoting patriarchal gender roles needs challenging, even if that group happens to be made up of transwomen?
No, can you point to any organised (political) group made up of transwomen who are promoting patriarchal gender roles? If you are talking about individuals and tumblr cliques then I guess the question would be does someone challenge transwomen more than ciswomen, or cismen? Because to do so - to treat a group differently, and more harshly, simply because they are trans - would of course be transphobia. I do not see the same energy poured into deconstructing Katie Price or any number of high profile macho men by trans critical feminists.
Am I a terf if I question how it is that a person 'becomes a woman' (or even stranger, just "is" a woman) when they have neither female biology (if that's relevant) nor any experience of the intensive gender-socialisation into a female gender role that women raised as women get?
No, not to question it. But to insist that anyone who does not meet a purely subjective definition of woman, which is not shared by everyone, has no right to ever organise politically as a woman, or enter a women only space, despite what other women might think, is trans exclusionary and that would make someone a terf.
Am I a terf if it appears to me that the word "cis" contains within it at the very least a strong implication that most people are non-coerced into their gender roles, are happy in them and that they constitute a 'natural' gender binary? (all of which assumption seems utterly wrong to me)
No, but to refuse to accept a linguistic need for a pragmatic antonym for trans, especially on the basis that there is no such thing as trangenderism - there are normal women and men who sometimes have 'pretend feels' - would be a characteristic of terf ideology.
Is it terf to reject the meaningfulness of the 'woman born in a man's body' narrative?
No, as I pointed out several trans people have done this themselves. But to reject the meaningfulness of gender dysphoria, or the meaningfulness of how some trans people report experiencing their bodies - to claim these things are delusions at best, or lies for some sinister rapey intent at worst - would also be a hallmark of terf ideology.
I don't think throwing terf around is particularly helpful because it is a highly ideological position which I'd suggest shares some common factors:-
That the gender binary is a social construct used to oppress biological women and to invert it reinforces rather than weakens the gender binary.
That you cannot change your sex and even if you change your gender (and parts of your biological sex) you should remain defined by your underlying sex - meaning presumably internal reproductive organs and chromosones.
That male to female transgenderism always has a sexual motive, either as a means to invade women's spaces and abuse women, or autogynephilia. As such transgenderism is a male sexual right's movement. Terfs don't tend to talk much about transwomen who are sexually orientated towards men.
That transwomen continue to display male patterns of violence and as such it is not safe to permit them to use women only services.
That female to male transgenderism is the result of the patriarchy causing lesbians to hate their bodies.
That trans inclusive ciswomen have been brainwashed by the patriarchy and need protecting by demanding on their behalf that all women only spaces become trans exclusive.
That transgenderism is an ideology designed to reinforce the gender binary rather than a way of how people have chosen to describe their lived experiences. As such the transgender phenomena is always inauthentic, trans people are liars or deluded.
That despite being mad, deluded, sexual perverts transwomen have enormous power due to their male socialization and have seized control of medical, legal, political and social institutions preventing any dissenting voices.
That transgenderism is a late 20th century western phenomena instigated by the pharmaceutical industry to trick men with a sexual fetish into buying estrogen pills.
That transgender rights and ciswomen's rights are always in opposition and that the growing social and legal acceptence of transgenderism represents the greatest current threat to women - and as such should be the priority of feminism. To counter this threat feminists should work towards morally mandating transsexuality out of existence using legal, social and medical means.
That such is the threat to women that any tactic can be justified no matter the harm such as lying to try and smear transwomen as sexual predators. Similarly any allegiance against transwomen is legitimate, even with the worst kind of patriarchs such as the right wing press and old school conservatives here and Trump supporting Republicans and evangelicals in the states. This is a fight for survival and so the enemy's enemy is always their friend.
I'd suggest anyone who appears to agree with all or most of this could be rightly described as a terf, and sadly that includes most of the women curently leading the fight against the GRA amendments.