Welcome! 1. Yes, it will be avaliable:
-I made a abstract model of the future script language for NPC programming http://wohlsoft.ru/forum/viewtopic.php?f=17&t=112
-Now ALL THE GLOBAL settings of ALL objects is in the *.INI-files, which is free to modify. I am making it all accessible for the freedom of editing of objects, and with INI files you can define your own NPCs with custom numbers for not replace the existing. I will use the *.ini configs for customizing global settings for each episode, and for each level, if you want. But currently I am coding the editor for a start. Before I make the release of the gaming engine, the editor should be useful as a alternate level/world/npc-config editor for SMBX.2. Yes:
-for using custom sprites, I am making a playable sprite calibration tool, and all points on the sprite (offset-X, offset-Y, height, width) defining in INI file for this sprite. And for characters I will make a parametric configuration for setting his(her) skills, speeds, jump forces, etc. And even the character's name (for a start, I am building the configuration that is compatible with SMBX, which has 5 characters).
But this tool I am making will be useful even for SMBX, for fixing wrong frames on user's sprites, but now I must capture all current physical collision boxes:For example:Source sprite:http://wohlnet.ru/sentfile/peach-3.gifConfig for this sprite: (collision boxes and animations for events)http://wohlnet.ru/sentfile/peach-3.iniCollision boxed for same sprite:http://wohlnet.ru/sentfile/peach-5.png
The sources of this tool is available on GitHub: https://github.com/Wohlhabend-Networks/PlatGEnWohl/tree/master/PlayableCalibrator
I am going to publish the release version of it later