Hi Namerie,
:think: I would say get something small 1 core 1GB RAM you can always upgrading it if you need.
Looking around at offers you will see so many technical and confessing terms biggest of all being the whole cloud thing which is just a fancy term for lots of servers linked together.
For a control panel what you choose depends on your end goal for the VPS do you want to be a hosting provider and have hundreds of accounts on it or do you want just a few sites hosted.
If you want to host and lot of sites I would go for cPanel, Webmin is very decent a free you want to keep costs down as it's FREE
CentOS and Debian would be my choice of operating system (cPanel only works with CentOs)
You say you want it for learning so I would recommend not even having a control to start with, you need to learn Linux on the command and everything about MySQL Apache DNS etc and be able to configure and maintain everything for the command line. All these control panels are just front ends for commands executed. For example you press the Reboot button in the panel interface all this is doing is issuing the command reboot. and they do more harm than good when learning imo. You must be able to understand whats happening in the background when a change, add or do something with a control panel. but the most useful feature imo is having an interface for customers to login to their account and manage things themselves like creating a mailbox.
You can still get a small VPS and have it fully managed for quite cheap under $20 a month and I would recommend management so you have someone to turn to for help when you have a problems or have someone to ask questions to about server configuration advice etc. Managed with most providers can be as hands on or off as you want.
Don't over analyze this to much and just buy it, but pay monthly so you can cancel if it does not meet your expectations.
TLDR version: $20 max 1 core 1 GB RAM with cPanel, Plesk or Webmin