6x2" is a fine size. In fact, some prefer no bigger for hand-held honing. As Brontosaurus says, it should come flat from Dan's, and need no lapping. You can check it across all dimensions with a steel ruler if you're unsure. They even lapped a 14"x4" special order primitive flat for me-I'm sure they do those 6x2's routinely.
I'm not Brontosaurus, but as for how to prep your surface, his advice is spot-on. You might even leave the "bottom" side as is and see how it does in a progression-it might surprise you. Given a flat stone from Dan's, some don't even sand or burnish their stones at all; they just start using them. If you want to tweak that surface a bit, you could get a flat tile or left-over piece of granite (a sink cut-out works great if you can snag one from your local granite installer for cheap or even free, maybe). Euclid/Marty recommends a dollar-store cookie sheet. Get an assortment of wet-dry sand paper up to about 1k (maybe save the 2k to see how you like it at 1k-many stop there and prefer that little bit extra cutting power). Wet-stick it to your flat, smooth surface and go to town, making sure you sand evenly by using figure-8's, flipping it around frequently, etc. You might need several sheets of each grit depending on how obsessive you want to get.
For my big black one, I cheated and used a power-sander, wet the paper and just moved it around, back and forth until the paper was loaded up. I even chamfered and radiused the sharp edges and corners with it very quickly (which is a good idea to avoid disastrous catches on your delicate edge). It worked even better than I had hoped it would, but I'm not sure if you would be comfortable trying that on a 6x2," especially if you have never treated one before. In either case, it is imperative to keep things moving evenly to keep your surface flat!
Once you have a uniformly-sanded surface, many of us like to burnish that surface with our heaviest, hardest steel tools. This is a great chance to tune-up your biggest kitchen knives, chisels, a hatchet or similar. This is another YMMV subject with many competing opinions. You can do a search on this and the other forum and read many pages of threads on the topic
I love the translucents, by the way. They have an almost waxed-glass feel to them that is just a joy to finish on-I like shaving lather on mine (though prefer WD-40 on my surgical blacks). Experiment and see what you like.
And don't forget to take it into the darkest room in your house and put a head-lamp or similar up against it-pretty amazing that a rock will pass light!
Post pics when you get it-Arks are endlessly fascinating stones!