First off, I don't think you need to make the front baffle 1" think, I used .50" and it is plenty, mainly because it isn't a very tall or wide speaker. If you are using a 1" baffle, be sure and cut some relief/round-overs on the back of the baffle, so the woofer can breathe.
Yeah, I know 1" baffles are overkill for the OS, but I'm also using this build to practice for bigger, more ambitious builds so I'm OK with going a bit overboard on this one. And yes, I am planning to chamfer the back of the baffle woofer hole.
I typically use butt-joints, with my only real design choice being the front and top over lap the other panels. So make the overall cabinet depth 0.50" short (1" in you case) to accommodate a full front baffle then make the sides and back 0.50" shorter, so the top panel overlaps those three (I just make the bottom fit inside the sides and back, so it is the smallest panel you cut). IMO doing it this way makes it easier hide the seems when you are finishing/painting, since people will most often be looking at the front baffle and top of the speaker.
Sealing MDF, I have seen 2-3 different processes. Some use Fiberglass resin, I have had a bad experience trying that one. I use the wood-glue/water method, or wood filler and auto body finishing putty with a razor blade methods most often.
If you are willing to trade some finishing time for assembly time, no need to use miters. They are quite difficult, unless you have the right tools and lots of clamps. Figuring miters also requires more patience and slightly more complex math. Another bonus to using butt-joints, if you cut one panel too short, just use it for the bottom panel.
Thanks for the tips.
I do have another question:
For those of you who do use miter joints, what sort of tooling, jigs, fixture, etc. do you use to cut long miters?