Yes, you can sell your own games. A game made with EasyRPG editor is not a modified source code of the software.
But remember the free software conditions: If you modify the source code of EasyRPG player distributed with your game, you need to redistribute those changes. If you sell via internet or via CD, you need to include the source code changes in the package.
You still can hold the full copyright over the game you made, of course if the game is made by you or you have the rights.
You can distribute it, sold or free (gratis), but you need to share the RTP replacement parts with their own license.
The modifications will have the same license as the RTP replacement. If you want the full rights, make materials from scratch or make edited or copied materials from public domain materials.
Of course, over your own parts. If the person just borrowed the free (libre) material parts of your game (player source code, RTP replacement material or derived works of them), it's legal because the license permits it. But if the person has taken your own materials under your rights violating your license, you can claim your rights.
Just talk with the creator of that material. That person is the copyright holder and can make a custom license for you.
Yes, you can. Remember you need to publish your source code changes if you make any modifications, sold or free (gratis), of a published distribution.
When you distribute the game, you generally distribute EasyRPG player binary. If the binary is not a custom version, you not need to distribute code of the player, you simply can link to the site including these binary and source (typically the official project homepage).
If the editor is custom is not a problem because you did not made a distribution of the editor part, but if you make a modification affecting both player and editor, you need to redistribute the source code editor part only if you distribute a binary part of the editor (generally you will not need to do release it, but it you don't release the binary, it would be a good practice to share the sources to the community) and you need to redistribute the source code of the player part if you distribute the modified player binary.
The player wants to be 100% compatible with RPG Maker 2000 and 2003. If the game work with the original RPG Maker 2000 or 2003, the game should work with EasyRPG. If the game does not work, EasyRPG is not completed yet or it's a EasyRPG bug.
No, we don't know about unofficial hacks and there are a bunch of them. Is hard to implement all of them without help or direct contribution of their authors in the EasyRPG code. Furthermore, there are few projects using these hacks, the priority is to emulate completely RPG Maker first.
The EasyRPG player works with the widely ported SDL library. The rest of the player are platform independent code. Just see if SDL is ported to that platform / operating system.
No, the EasyRPG editor only will import games and it will save them on a new, extensible format, supported by EasyRPG player.
Is better to work on a new format because we can do anything without limitations. For example, we expect to make individual files for each database entry instead of big files, for easier sharing of resources between game developers. For example: data/actors/0001.xml (or any other extensible format, XML is just an example, too).
Yes, but the first goal is to fully support RPG Maker 2000/2003 playing. The editor has less priority until the full emulation is done.
The editor depends a lot of the player source code and it needs to be stabilized first.
When it will be done.
Of course, if you contribute with the project, probably the project will be completed sooner. The most interested people in complete the project are working on it to make it possible, why you don't?