Ive been developing software for several years now. You and everyone plus their brother wants to make a rpg. Simple answer DON'T BE STUPID. A game engine is not a gateway to perfection. You need to know how to program before using a engine. Every engine will be written in a language which you should know BEFORE using it or at LEAST have a good grasp on programming logic. In your case you have none. You need to spend about 6 months or so learning a good easy language like c# and then go grab a good engine like Unity or something simular to c# language based engine.
A RPG is the hardest and biggest game to develop in most cases. Trying to fly into space with a bicycle an't going to happen. You have to build up to something lke a RPG program. There is NO fast track for learning logic and programing. The world would be a better place if the industry was not plagued with people trying to make the next Wow. Seriously this is whay their is a 80% failure rate for projects. Not trying to be harsh but seriously you could ask 10 people if they want to make a rpg and 9 out of 10 would say yes lets start tommarow. Don't fall into that group, research something before trying to attempt it.
- Is it necessary to have a cinematic?
No. This is not even common pratice unless your a large company.
- Is it important to put the trailer on television?
No. How many indie games do you see on tv, likely none.
- Do I need to give a convention about my game.
Ahh .. no, I'm sure all the Star Wars fans wont be upset.
- How much does it cost to put a trailer on television that takes around 30 seconds?
Depends on the time of day. Prime time is very expensive but later hours can be very affordable.
- How do I create a trailer on the gameplay? Do I need to introduce myself the first seconds in the video or first start with the game itself and then introduce myself and explain how the game works?
No real answer, I suggest game play with voice over.
- Do I have more chance to make it sell with a free demo version?
Yes, always offer a demo.
- How do I prevent the possibility of pirating my game?
Nothing you can do really, it will happen no matter what at some point if your product is successful.
- How do I reach the market? Like how do I get my game in a store? Where do I burn all those cd's with my game?
Ahh don't go down this route. To be honest this is a money pit unless your a big company and willing to spend millions and can aford to make 2 cents per copy sold.
- How can I make it clear in the first game that there is a possibility of a second game based on the first one? Or an expansion.
Website, Facebook and other social media forums are good ways to clue your fan base into a expansion.
Just a tip. Making the game is step one. Many think once they finish a game, they are done. Not true, after development is perhapps the hardest part of software development. For my self its a breeze but I also have a degree in business and in various other fields. Marketing/learning how to market your product will truely tell you if your going to be successful or not. Networking as well proves to be hard for some. The best thing you can do is hire a Pr person or profit share witht hem if you can not afford to pay hourly. I hope this helps.
You can not copyright or patient a concept or idea. You can copyright/patient your source code. This is your only real legal protection aginst "cloning". However, others can make simular products based off your concept/idea but it can not be identical.