A nice stone is a double sided 'hockey puck' synthetic stone. The norton version is 3.5 inches across and 220/600 grit I think.. about 20$ or so. You can find em sometimes a bit cheaper, dunno quality.
For a hawk you don't really need it, it's awfully nice on a big ol double bit axe..
most hawks are sharpenable with a fine file and cheap whetstone just fine. As with any hatchet, the sort of wood you intend to cut determines the type of edge. A kindling hatchet will be sharpened a bit shorter and less beveled than one intended for evergreens. you'ld use a VERY short edge on a survival tool, likely, to make it sturdier, and a long thin edge on one intended mostly for skinning and to replace a camp knife.
How to keep it sharp is a tricky question, cause obviously the BEST way is to start with one that stays sharp longest.
The type of steel used determines that, and very little hawk steel (with the exception of handmade/top end custom) is worth discussing. Almost all of it is either bulk stainless, which is almost all junk, or bulk carbon which isn't a LOT better..
If it's decently forged and heat treated, you can get a reasonable tool out of less than perfect steels, but it won't STAY sharp nearly as well as better quality.
So, on a one shot .. keep it sharp by buying great steel. On a more immediate note, sharpen it to the task.. and carry a small hone of some sort and touch it up regularly.
Long term, a hockey puck stone is pleasant and fits the job..