I wouldn't bother with thinking about it in terms your first point. Old-school vs newer isn't really relevant to the comparison you're looking. Crossdressing is something that has a clear definition - dressing in a way that is contrary to the societal expectations for your gender. As you mention it is also more of an objective non-sexual term.
Sissy is a lot more ambiguous and tends to mean something different to each individual. Because of this it's going to difficult to get a clear answer. It's a term that, in the way you're referring, carries a clear sexual implication and usually in my mind comes in tandem with idolizing/embodying feminization(not necessarily crossdressing) and has D/s BDSM roles baked into it generally.
At the end of the day though, do what makes you comfortable and don't worry so much about labels.
Very good points all around! I'm pretty comfortable with where I'm at but it's always good to read someone summarize it as well as you did.
Crossdressing isn't inherently sexual, being a sissy is in almost every case, sexual. Many if not most crossdressers are straight, most sissies are at least a little bisexual. Crossdressers look at the clothing they wear with pride, it's an entirely positive thing. For a sissy, the frilly dresses and such are mean to demean their manhood and provide the humiliation that most sissies crave I have also found that while nearly every sissy is submissive, many crossdressers are dom or neither
I think a crossdresser is someone who wears clothing typical of the opposite gender, while a sissy is the male equivalent of a tomboy with a little stigma attached. These definitions would mean most sissies are crossdressers and many crossdressers are sissies
You're not alone in this and I think this is natural for anyone figuring out their identity on the trans/enby/cd/fem-spectrum. I'm also still figuring things out and it's okay to defy categorization.
I've researched some angles and I'd like to share them with you:
I think what many of us in this community might experience is some form of autogynephilia. We derive some sort of pleasure from seeing ourselves as feminine. It can be especially difficult to find the difference between this and any form of gender identity other than your assigned sex at birth because the lines tend to blur sometimes. While theory states autogynephilia is by definition sexual in nature, I think the mechanism also exists for nonsexual feelings coming from the same principle where a feminine version of yourself is the source of positive emotions.
But let's not rely on theory on sexuality too much, let's focus on what's important, which is who you are. Not who you're attracted to. Attraction does matter, but it's secondary to your own identity.
Starting with my current understanding of myself, this is my interpretation of Fluidflux. See, the "official" description does not quite align with my experience. The best way to describe it is to look at gender as a finite number of "skill points" (because games are always a great way to model reality). Some days my build is purely FEM, while other days I'm rocking a more balanced build between MAS, NBI and NUL. I like all those gender identities and I feel that it's fine to just flucuate between them in various degrees for the time being. You might say "that's just genderfluid" and you might be right, but the fluidflux flag is just way cooler.
Either way, I consider both crossdresser and sissy to be part of who I am, but neither paint the full picture. It all depends on what you enjoy and you can be anything you want kinda thing.
Your take on crossdressing is exactly right, it's an expression of your tastes in clothing. You wear feminine clothing because you want to and the reason why might be strenghened by kinks, a feminine gender identity or just your fashion sense. All are valid.
Sissy is a kink, and while I'm not really fond of the word itself, the main elements of the kink I do agree with. It is focussed on sex, where you are either on the receiving end or on the submissive side of the power dynamic. I don't think it needs to be exclusively men, but it seems that part of the fun is for people to discover their attraction to the concept of sex with men this way and deriving excitement from something that will stay in a grey area until they accept that 100% straight is not a thing. To me, it is mostly about taking the role traditionally fulfilled by women in straight relationships and doing so either voluntarily, or with help (hypno, coercion, force, etc).
But the main takeaway is that everyone is different and everyone will cherry-pick different aspects of popular concepts to form their own identity, and that is what makes us beautifully diverse.
For relatability I'll list some of the things that make me who I am: