Is it advisable to file a provisional patent now, based on how I've built the prototype?
But more accurarely, it seems useful to consider the difference between a product and an invention.
When you build a prototype, it may implement one or more of your inventions. There was be one invention in the means for connecting the bits connect together, another invention in the orientation of one of the components, and a another invention is how the parts interact to do something surprising. Each of these inventions are separate, even though there is only one product.
When you have developed your invention such that you know how the invention functions and that it's sound, you could reasonably file a patent application. It doesn't matter how your prototype is: that's just one implementation of your invention.
You have mentioned that your product needs a bit of refinement. That's obviously important for actually selling a product, but that may or may not be related to whether your invention needs refinement. There is usually no benefit holding off filing a patent application based on how your product is progressing, unless there is a reasonable chance the invention itself will change.
In any case, I should note there is some facility to add in additional features in the 1 year between filing a provisional and filing a non-provisional (either by filing a second provisional, or when you file the non-provisional). While this has disadvantages compared to filing everything in the provisional (such that you wouldn't intentionally rely on doing so if it could be easily avoided), it can be useful.