I'd suggest going with Dropbox and/or Google Drive... Mediafire has been a scourge of ad-evil and I don't like how MEGA takes liberties on how things get downloaded. This is talking from the consumer side of file retrieval here. If you have access to your own website eventually I'd recommend planting it there also.
Editors that are popular for folks here making some of these wacky packs.
Gimp (Linux, Win, Mac), Paint.NET (don't confuse with MSPaint) (Windows only sfaik), Inkscape (Linux, Win, Mac)
(if you can afford it... Photoshop is nice but a bit excessive for pixel work... would only recommend if you've got the tools for digital painting (wacom style tablet) and wanting to pull some HD painting stuff)
Krita's gaining a touch of momentum here too. From how it feels... I get a bit of a Corel Painter feel from it with less gamekilling bugs. It also has an auto-tiling feature (that I've not found how to use yet but still tinkering XD)
Best of luck to ya, do post your developments.