Few things to keep in mind--
That sealer stuff you're now into it is supposedly very toxic, like really toxic. You don't want to breathe it. So if you're dead set on sanding through it you should definitely get a real respirator, not just a dusk mask.
Secondly, unless you're going with a transparent finish, you don't need to remove the sealer. Many skilled painters will go down to the sealer and prep/prime over that. Actually, some good guitar painters don't even strip the color coat off -- if you know what you're doing, you can prep and prime right over that. Obviously I'm not a believer in the various theories about the tonal benefits of nitro over bare wood and am not really interested in starting that debate -- there are advocates both ways. Plus you'll probably never get the grain sealed as well as the factory did it, unless you're really experienced with grain filler and sealer and know what to look for. I see a lot of refins (including some of mine!) where the grain is still visible.
Finally, you may be surprised at how much wood you have to remove to get all the way through that stuff, as you would need to do if you're planning on some sort of stained or transparent finish. I did a JS
body awhile back and was surprised that when I was all done, the cavity covers would no longer lay flush because they wound up sitting about 1/8" above the body. I then had to re-route the narrow shelves that they rest on to fix the problem. You may THINK you're all the way through it and then wind up with a blotchy finish when you start to apply the stain. I've also seen a lot of those "almost got it" refins.
Those are my humble opinions. I'm no expert, but I've been through this a number of times and know what you're dealing with. Whatever you do, have fun!