I've been enjoying playing on the server so far. I've found a really nice spot on this map, and 1.13's ocean mechanics are fun to mess around with.
I'm a bit concerned by the amount of lag on the server - people don't have much built yet and the TPS is frequently below 20. Perhaps you could use a java profiler to find which plugins are causing it?
I don't really see a purpose to the Cemetech Gems. They are too valuable to make small transactions in - on the last server, lapis ore was worth 100 denarii, and the ore spawning rates were increased in the ABBA world. Many shops sold stacks of items for significantly less than that amount, so in order for a transaction to equal a whole number value of cemetech gems would require the buyer to buy many stacks of items. Because of this, players have mostly been using a barter system to exchange goods. The gems are also tradeable for non-renewable items at spawn, but this is also somewhat irrelevant because the gems themselves are non-renewable - you could just get the non-renewable items you would be trading for from the ABBA rather than getting ores from the ABBA and then trading them later.
EDIT type thing because I got ~ninja'd: Why use a plugin when we could have players come up with a redstone solution for shops? It could pose a fun challenge.
I feel that the map size is too restrictive - there's no way to get mobs like mooshrooms or cats. Allowing portals to be used like Dnar suggested would allow these mobs to enter the main world, but it wouldn't allow players to build farms for these kinds of mobs.
EDIT type thing because I got ~ninja'd: It should be possible to use multiverse to link two overworlds to one nether - if not, you could always leave a portal back to the main world at the spawn of the abba.
Kerm also seemed interested in
this plugin, which causes minecarts to act like trains. It would be cool if we added that.
A few more minor suggestions for data pack recipes which don't deserve their own posts: Maybe shulkers could respawn over time, the dragon could drop elytra and dragon eggs (which no longer break bedrock in 1.13), husks could drop sand, sand could be dyed red with red dye and red dye could be made into normal sand with yellow dye, turtles could drop gravel, drowneds could drop clay, obsidian which smelts while there is a empty bucket in the fuel slot produces smooth stone and fills the bucket with lava, cobwebs could be rarely dropped by spiders, and two sand plus two coal and two soul sand makes four soul sand.