He's pretty much a household name, so you can go with the typical Oxford, Penguin, Everyman's Library or Modern Library if you like
Also, these are not bad if you like the cover art; no specific reason to buy them other than the covers, though
There aren't huge differences in translation from one to another? Even over the years? I wanted to check out some used bookstores so I might find older editions of Kafka's work.
Any collections I should keep an eye out for with short stories?
There are differences, yes, but with Kafka i've found they just can't really be resolved, you know? Like the only way you can avoid them is by reading him in German. Some people on this board probably have a consistent or inconsistent favourite among the first four publishers I mentioned, but generally speaking they're all top-tier in terms of the translators they employ.
Given that Kafka stopped writing a very long time ago, most publishers who have one will have all, probably done by the same translator.
Most series have The Castle, The Trial, Amerika, and an anthology of his short stories. The one I posed a pic of (Deckle Edge) also published his Diaries, Aphorisms, and both a complete and partial collection of his stories
You're best off getting the Schocken editions. The Muir translations are enjoyable in their own right, but the Schocken editions have the best modern translations. I'm personally not too into the Anthea Bell Castle or the Hoffman Amerika.