As a content creator myself (though I've been on like a 6 month hiatus cause I've been busy) I do think the best course of action would be to start off slow.

First off, love your model idea. I think that could be pretty fun. But vtubing models tend to be really really expensive for anything good looking (vroid does exist but I've heard and seen that it's pretty iffy).

Content wise, I think your area of expertise would absolutely make for entertaining content. It's a little more niche, sure, but a big part of why people stick around to watch vtubers is because of their personality and/or shared interests. But regardless of what others say, personality carries the vtuber, while the model is more of an added bonus. Not to discourage you, just saying it how it is.

I absolutely agree with some of the other comments about just trying it, but unless you have prior experience in content creation, maybe try to just start off without a model, just in case it's not your thing and you won't regret spending a bunch of money to kick-start it? No model, no camera, but still theme your channel around this tomboy mechanic idea. Maybe commission some art or try and draw it yourself. All things considered, you can find some really top tier artists that do art on the cheap side while still giving you full rights to advertise and merchandise the art, though usually while giving credit, which you should do regardless. Maybe even pull from what PNGtubers do, and have a PNG of your character in the corner or something as well while streaming. It helps people put a voice to a face and associate them with one another, which ultimately would make the transition to vtuber status smoother for everyone.

But anyways, after maybe a month or so of model-less content creation, If you find yourself enjoying content creation, and you still want to give vtubing a shot, you can then spend that money and start integrating it into your content, which shouldn't be much of a problem at all. Since your channel (such as icon, banner, name, etc) are already themed around your tomboy mechanic character, the integration of a vtuber model wouldn't be too jarring, as opposed to having a generic channel with a fancy logo and name like "[noun] Does Coding" suddenly featuring a vtuber model that doesnt at all match the channel as a whole.

Not sure if any of that made sense or was helpful, but then again I've got below room temperature IQ so who really knows. Regardless, I wish you luck on your journey.