Add more signs to the Farm shop at /warp shop allowing you to sell more than just 64 at time.
Having the ability to right-click harvest/replant would be an amazing thing. Additionally, have an enchant for hoes to make you get more OR having a scythe that can harvest a 9x9 area at once, would be great! There are many plug-ins out there including:
https://dev.bukkit.org/projects/farmingupgrade
https://marketplace.songoda.com/marketplace/product/epicfarming-ultimate-minecraft-farming.21
These are just a few that I found but I'm sure there are plenty of others out there. Or you can make your own.