I could try the top two but the art program is impossible in GM : S, as I don't think that there is a way to program it to save and open pictures :/
Really nice suggestions there, I'd love to try at least one I'll put up the poll.
What do you mean by this in the years i worked with GM:S 1.X I never had an issue with loading images from folders or from inside the IDE using the draw_sprite. You can also use draw_sprite_ext_colour for many more options or just draw_sprite_ext.
you can load a png file using sprite_add(fname, imgnumb, removeback, smooth, xorig, yorig);
It will allow players to add things into a game from an external source or for you also.
You just fill in the required fields. There are ways to make it so you don't have to put in the name of the files to be a specific file name to allow for "modding" by the player just in case they don't name it to the specific file name. Make sure you use sprite_delete when it's no longer needed to prevent memory leaks.Edit:
In order to do the paint program you can use surface_save which will save a surface to a png or other file type supported.Surfaces are easy to learn and use and allows for a lot. You can create the grid for them to draw on using a ds_grid. This will allow you to only draw in certain areas defined for this program. They are also very useful for storing data as a 2D array. Also check out the for loop, and all the DS(data structure) functions.
There are a few people here who use GM so if you have any questions or issues search the net for a solution or check the docs then if that don't help just put it here crab and i can help you. Make me last resort though as its good to figure things out on you own.