I can't speak for Dave, and won't presume to anticipate what they would say to your questions. I do have my own thoughts, however.
I think the issue as you have framed it puts the cart before the horse. I don't know anyone experiencing dysphoria who wears something to feel more feminine or masculine (or anything else, since there are several genders). I do know many people, however, who experience dysphoria and where something that more matches their concept of how they should look.
In other words, dysphoria is innate, standards of what makes appearance masculine, feminine, etc. are not. Those are determined by society. Before I transitioned, while society still took my outward appearance to be coded as masculine, I would bristle when called "sir," or when the title "Mr." was affixed to my name, because that wasn't who I was, regardless of what I looked like to others. And, in fact, if I put on a pink dress but did not change my outer appearance--especially body proportions--to fit who I really was, I would have just appeared as a man in a dress and probably would still have been "sirred."
Two morals to that story: 1) regardless of whether we want it to be that way, society has coded what it means to appear masculine or feminine (even to the extent of putting those who are neither in one of those boxes); 2) Gender transcends what society judges to be masculine or feminine appearance.
Before transition, society coded me as a man and treated me accordingly. It didn't matter what I was wearing, the other cues--slim hips, flat chest, short(ish) hair, deep(ish) voice, etc.--tipped the scales toward masculine whether I wanted to give that impression or not (I didn't). If wearing a pink dress had coded me as feminine in society's eyes, that would have been great because I already saw myself that way. I would not put on a pink dress and expect to feel more feminine, though. I would present more feminine so that others reacted to me in the way I already knew myself to be.
That brings me to the second point. My gender exists regardless of how I look, what I wear, or how others perceive me. The fact that my body has changed since my transition so that it more closely reflects my actual gender is all to the better. But let me be clear that I did not change my appearance to feel like my gender. I changed my appearance to more closely match my gender. Notice that dysphoria is a conflict between the gender we have been assigned at birth (frequently based on the appearance of our genitals) and our actual gender (which sometimes exists in contradiction to the appearance of our genitals). Dysphoria is lessened when I am able to look in the mirror and see the woman I know I am instead of the man society told me I was for decades.
In other words, what I wear doesn't dictate my gender, but my gender might dictate what I wear.
Now to your hypothetical question. I don't think I've met anyone who is both blind and deaf, but I do know some trans people who are blind. At least one of them was blind at birth, so she probably would be a good example for your hypothetical question. It sounds like you feel that someone who has never seen what society codes as feminine would know to appear feminine. If so, you would be incorrect in the case of my acquaintance. Although she does not dress "high femme," she would never be coded as masculine. She lives alone and does not have someone to dress her or do makeup, but if that weren't the case, she may very well look even more feminine than she already does. Other blind trans women I've met do have personal assistants and look very feminine.
And yes, you could say that someone with an assistant is relying on someone else's definition of what looks feminine. To an extent you are right, but she relies on someone else's concept of femininity no more than everyone does. I don't know what you look like, but I would predict that your appearance is, in one way or another, a reaction to how society thinks your gender is supposed to look. Even if you were to present in a style society codes as masculine, you would still be doing so as a reaction to what the rest of society thinks is masculine or feminine. And if you were to present in a way that is ambiguous or reflects a lack of concern for how others perceive your gender? You are still doing it in reaction to what others see as the appropriate gender presentation.
And that brings us to how someone who is deaf and blind would present in terms of gender. As I said, I have not met anyone--trans or cis--who is deaf and blind. I do, however, know something about a famous person who was deaf, blind, and unable to speak: Helen Keller. Because of her own writings and appearances, and because of the observations of those around her, we know that she coded as feminine. The time period in which she lived was much more rigid about masculine and feminine appearance so we would know if she wore clothes not associated with women. Even if she had, we also know that she embraced the pronouns "she, her, hers," and thought of herself as a woman. In other words, without being to see, hear, or interact verbally with her society, she was able to experience and manifest gender.
As I said at the start, I'm not sure Dave will respond to your questions or what will be said if so. I do know, however, that asking if someone would experience gender were they deaf and blind is not the difficult question you might think it is. Witness the examples I've just given.
Thanks for reading (hopefully you did read this far!),