--> What is Ren'Py?

Ren'Py is a visual novel engine that helps you use words, images, and sounds to tell stories with the computer. These can be both visual novels and life simulation games

--> Is Ren'Py easy to use?

Yes, for most part Ren'Py is very easy to use. But it does get complicated as you dive deeper into Ren'Py because for implementing those complicated system, you will need intermediate knowledge of Python and PyGame.
But as a casual developer, you would never ned to go that far, and even if you do, the lemmasoft community and (hopefully) we will be here to help you.

--> What other software do I need for Ren'Py?

None; Ren'Py comes with every software you will ever need, But you do need Java and Direct X (for windows), but then again, everyone has those.
But if I by any chance you don't have them, you can download them from here.
Java: http://java.com/en/download/index.jsp
Direct-X 9.0c: http://www.microsoft.com/en-us/download/details.aspx?id=23471

--> I don't like JEdit, are there any other editors I can use with Ren'Py?

You can use virtually any text editor with Ren'Py, yes even Notepad.
There are a few ediors on Ren'Py Wiki http://www.renpy.org/wiki/renpy/Editors
And PyTom (creator of Ren'Py) is working on adding official support for Editra (another editor).

--> What are the minimum requirements for running Ren'Py?

Any modern PC should be able to play Ren'Py without any trouble.
The lowest specs I have tested Ren'Py on are:

RAM: 128 MB
Processor: Pentium 4 1.7 GHz
OS: Windows XP SP1
Graphics Card: Intel integrated chipset

--> Can I develop iOS or Android games using Ren'Py?

You can develop games for Android but you can't develop game4s for iOS using Ren'Py.

--> Are any other mobile platform supported?

No, except Android, no other mobile platform is supported.

--> Can I use flash in Ren'Py ? 

No.

--> Can I use animated gif images in Ren'Py?

No, there's no support for animated gif image. It's an obsolete image format and you can use ATL to animate images.

--> Can I use Ren'Py for creating a dating sim, RPG or other type of games?

For dating sims you can use a Dating Sim Engine framewok http://www.renpy.org/wiki/renpy/DSE

For RPGs there is an RPG battle engine - http://eviscerate.net/article/rpg-battle-engine-renpy
The RPG battle engine is for non-commercioal use only and is in alpha version.

In order to create a proper RPG or other types of games, you will need to create your own engine using Python code and Py'Game library.

--> Can I make a 3D shooter in Ren'Py?
It would be possible, but pretty much pointless. Since Ren'Py supports Py'Game a very basic 3D shooter would be possible. However, doing it in Ren'Py, this would require a lot more effort, than using a more appropriate engine, with wich you can make a proper 3D Shooter.