Likely more generic things but that have a theme. So bunches of mermaids but all of them wear glasses, or all are at sunset, but all look different in design not just poster composition.
I recommend if you have Facebook looking for the "Artist Alley Network International" group.
If you don't have to worry about money to purchase merchandise, then yay. But I do recommend purchasing bags to put your merchandise into so it's protected at the convention floor after people buy it. I recommend this website since you can buy a million different kinds, in different sizes, and all of their products are amazing quality.
https://www.clearbags.com/bags
Lastly, just because you "plan" to sell at an anime convention "next year" keep in mind that most AA's have strict rules about getting in. Anything from requiring Business Numbers, tax numbers (USA), first come first served, juried, and a million other constraints. If the convention has a "small press" area to sell at as part of the AA but isn't "exhibitor" I'd suggest going for that since you won't have fanart. The tables are usually more expensive, but you'll be placed usually somewhere not in the sea of the AA, and in the case of them being in a different room from the Exhibitor's Hall (a new thing in the last few years as conventions attempt to battle company's like Crunchyroll's stance on fanart due to copyright issues), you'll be likely placed with the EH, not the AA. You can also opt for the EH again as you aren't doing fanart.
AA tables can cost around 140$
Small press can cost 260$
EH tables 350$
Those are just some example numbers that I recall from looking at Sakura Con (seattle washington, easter weekend) and Kumori (portland oregon, halloween weekend). Other conventions charge more or less. Always be wary of conventions that charge too much for their event (ie a table costs 80 at a young or not established event, or it costs 200. the 80 is usually agreeable but kind of high, and 200 is ludicrous)