My first server

[MXan]

So I've followed some tutorials and tweaked with things until it almost works... almost. If someone could answer these questions, I'd be much obliged. I posted this stuff elsewhere, but realized this was probably the correct place to post this in the first place.
1) What is a datapack?
2) Is there an easy way to add NPCs, specifically for buying/selling?
3) I can log in to an account and player, but changes are not kept. As in, I go kill a rat, log off, log in, and my character has 0xp and is back at the starting location. How do I fix this?

(I'm using TFS 2.13 x64 GUI, Client 9.54, OtLand IP Changer, XAMPP 1.8 x32, XAMPP control panel 3.0.12)

Thank you in advance!

 

[Mark]

1) A pack with customization in the data directory.
2) Adding them using shop_buyable and shop_sellable parameters in their XML file is easy enough for me.
3) Update to Patch Level 1 of 0.2.13, that bug was fixed.