Downloading others' creations is a thing, yes, and its a part of 0.19 which dropped today! OwO
There is no dedicated site per se, but there is a dedicated (and moderated) Discord channel for this purpose, on our discord server. Tacky? Yea, but it's free.
Roadmap: Yes no kinda? I maintain a todo list that only the devs can see. I don't prescribe to a solidified roadmap because I am constantly changing the order in which I am doing things depending on what I overhear people asking for most. So instead, i have a list of things i want to do that is constantly being added or removed from, and the priority order of the work is constantly shifting.
Pictures/art: Eventually? Unfortunately I am the sole programmer AND artist for the game. Working on one means subtracting time from the other. I am also still learning art, so the results aren't ideal.
Support: You can now support by writing content for the game! Also you could share the game? Not a lot of people know we're doing a thing here XD