Yes, you can set an uploaded world to be your default world ("spawn world"). In order to do this, make sure that you have Multiverse installed (you can get this from the Plugins tab on your Minehut control panel), once you have Multiverse, you're going to want to go into your game and, firstly, execute the command: /mv conf firstspawnoverride true -- this will ensure that the spawn world (which you have not yet set) will override the original world. Next, you're going to want to set your spawn world, using /mv conf firstspawnworld {world name}
As for datapacks: yes, it's completely possible to use datapacks, however, considering that the File Manager doesn't have a bulk upload feature, you'll need to add each file from the datapack manually.