I am a bit confused, you say you "love game development". Does this mean you have previous experience programming games or do you mean you like the idea of game development?
Anyway that aside, I went ahead and looked at Tibia. The company owning tibia have the following requirements for a job as a software engineer:
- Completed a computer science degree or equivalent training
- Very good knowledge of object oriented programming (C + +, C #, Java)
- Good knowledge of software design, algorithms and data structures
- Good knowledge of databases and network programming
On a game like Tibia there will probably be more than one programmer so the work will be distributed along them. If you want to "start to create a 2d isometric mmorpg like tibia" you are going need to be on par with those points and it will take you a lot longer since you are only one person. Why did I post this? Because a lot of people new to game development think that they can achieve miracles in a short period of time. The reality is you are going to spend a lot of time learning a programming language, a lot of time learning new technologies and libraries and a lot of time about game structuring and architecture. It's a hell of a thing.
The purpose of this post is not to demotivate you, you can surely get to that point. But you are going to have to start smaller. Learn through experience and use that experience to build bigger projects.
As I said, I don't know what your experience is when it comes to game development, or even programming. So maybe I am wrong and you know exactly what you are doing, thus I will just answer the questions you gave:
1) You will find arguments on every post on which is better to use, do some beginner tutorials with each one and decide on that.
2) The map editor will probably save the data in a user file format and the game engine will read the data. Sorry, I don't know anything about networks and games.
3) SDL -> Simple Direct Media layer, it's a library that allows you to program games by giving you modules to easily display graphics and other game related functions