General

In this case what would it even mean for you to be a BBW? Just identifying as such? You would still be a biological male, so if it's mostly the body of a BBW what you're after, you won't get it merely by identifying as such. You could do extensive and risky plastic surgery, but even that won't give you the body of a BBW (proponents of such surgeries often over-exaggerate its effectiveness, because it's a lot of money for them in it, so of course they hide the drawbacks and present it as "perfect" ), and it's almost impossible to undo if you later change your mind.

Your fat distribution won't change by just identifying as female.

Would roleplay be an option instead?

Please ignore the transphobe.

Gender envy is a complex thing. It sounds like you are still figuring things out. My advise is to experiment for now. You already know that femininity arouses you, but you aren't sure if you are trans. Try being girly when you aren't horny.

Start small (growing your hair out, shave your body hair, dress like a woman in your home and go about your day), and move onto bigger and bolder things. As you socially transition, you can decide if you are actually trans or if it's just a kink and go from there.

My advice is to experiment a lot. You have plenty of time to decide your gender, have you tried using gender neutral?

Have fun with this fetish and if you still have doubts visit a psychiatrist to help you find your way.

Trying to understand what one really wants is "transphobia"? Not instantly and blindly recommending full-on transitioning when the first thoughts appear about the topic is "transphobia"? Recommending people to first study themselves and their desires a little deeper before they make changes to themselves they later can't undo is "phobia"? Do you even know what that word means?
Don't be a such a jerk!

I do know what it means. My issue isn't with you telling OP to figure out himself before making a choice. Well all told him to do that.

My issue is with you using anti-trans talking points to do it. Do you realize that people say these things to trans people all the time to negate their gender identity. Whether or not OP is cisgender or transgender is besides the point.

For the record, this is what you said. There are trans people in this community who hear things like this all the time.

Again, there's no problem with you telling OP to figure himself out. It's the best piece of advice to give him. It's all the extra things you said that creates the problem.

If a guy who has never even suffered from gender dysphoria says he wants to be a woman and asks for advice, then it's a logical question to ask what exactly it even means to him to be a "woman", and what qualities of a woman is he really after, because people are different and answers might widely differ. (hey, that's a meaningful question to ask regardless of the antecedents). Without that, there can be no meaningful answer or advice.

It's much more despicable to just cheer such people up without thinking and peer pressure them to just go ahead (while name-calling everyone who doesn't do so), as a form of virtue signaling. We often see similar things around here when someone announces of thinking about becoming immobile. There is a crowd cheering them to go for it, because doing so satisfies their kink and that's more important for them than what happens to the other person. Thankfully, in the topic of immobility, now there are some reasoned voices, but in the trans case, there isn't. As soon as someone has even 1% doubt about their gender identity, a crowd shows up cheering for transitioning, as if they were a cult and applying peer pressure. And me not joining that cult doesn't make me a transphobe. Just like not cheering someone for becoming immobile doesn't make me fatphobic.

And I don't care about who has used what talking points (as long as they contain no expletives or otherwise highly offensive language). For example, if I believe that 2+2=4, then just because someone who I don't like also says it, be it even freaking Hitler himself, doesn't make it false. And if I know for a fact that surgical procedures carry a risk, I won't lie and pretend out of ideological reasons that they don't.

First I admire your bravery. Thats a big step. A big invest of time resources and energy. Be sure it is what you want to do before you take the step. If you do you will find support in this community.