Gender is a system of socially imposed behaviours based on physical or perceived sex.
I think we can almost agree on this. I'd say it's socially expected behaviours rather than imposed though, since we are under no obligation to comply with them.
Gender identity is where we feel most comfortable within that system regardless of physical sex and may also indicate how we internally experience our sexed bodies within a gendered system.
Now this is where we disagree. I just behave as I wish, according to my own personal preferences. I am aware that some of these behaviours comply with what is expected of women, but many of them don't. I don't view this as a 'gender identity', but simply a personality. To describe these behaviours in terms of a 'gender identity' appears to me to be reinforcing sexism and the idea that certain behaviours are only acceptable for one or other sex. In other words, 'gender identity' seems to be reinforcing gender stereotypes.
I'm not going to comment on 'how we internally experience our sexed bodies within a gendered system' because I don't understand what you mean.
Gender presentation is the social codes we adopt, both consciously and unconsciously, which indicate our gender identity.
Again, describing the way I dress or other aspects of my appearance in terms of 'gender' is reinforcing the notion that certain presentations are only acceptable for one sex or the other. A progressive society would accept that people don't always dress in accordance with outdated stereotypes. And obviously, what I wear or other aspects of my appearance can't be construed as indicating my 'gender identity', since I don't have one.
Personally I say abolish it all. But until that is achived it seems most humane to allow people to live accordance with their gender identity. Probably being humane is a bit too close to being kind for some of you lot. But that's what I think we should do.
I think it would be more humane and kind to say to everyone 'dress how you want, live how you want (as long as you are not harming others), but you can't change sex'.