I should be releasing a few bug fix versions over the next few weeks. We'll see after that.
Tile support is being added over time. You can currently customize the creature tiles, though the only picture that currently comes with the game is a miner. Other game elements will be supported in the future. Tile sets created by the wiki community can be found here, and fonts for these tiles sets are here, near the bottom. See data/init/init.txt and raw/graphics/graphics_example.txt for more details on how to add your own graphics.
There are more pressing things to do right now.
According to DF player Jonas, DF seems to work flawlessly with Wine (0.9.2.9) under Linux (Gentoo 2.6.19). No special setup required. Map was built in about 8 minutes (AthlonXP 3200+, 2GB RAM). There's more information at The DF Wiki FAQ. The Wine application database entry is here.
This depends in part on the porting of Kobold Quest. As soon as somebody ports this and releases it with a suitably permissive license, we'll then try to do the same with Dwarf Fortress as we are able. Kobold Quest and Dwarf Fortress are based on the same engine. The relevant forum thread is here. I currently have a tentative Linux port of Kobold Quest, but do not yet have proper license information for the code.
No. We don't want to associate with other people at a quasi-professional level, since this would make development less enjoyable. This is not a job for us; it is our personal mission.
No. Heavily diluting Dwarf Fortress adds a strong element of unpredictability to our support, and your donations are our sole source of income. While donations might not be affected at all, it's not a risk we can take at this point if the project is to continue.
We are not taking submissions, but you can share them with others at the Forums and The Dwarf Fortress Wiki.
There is information at the support page.
It depends. Version 0.27.169.32a breaks compatibility with older versions. There are instructions at the top of the file "release_changes.txt" that comes with the download.
Open "data\init\init.txt" and change the line "[VARIED_GROUND_TILES:YES]" to "[VARIED_GROUND_TILES:NO]".
Open "data\init\init.txt" and change the line "[SOUND:ON]" to "[SOUND:OFF]".
Go to the Forums and ask away! You might find the information you seek has already been posted. You can also try The Dwarf Fortress Wiki, which also has a more extensive FAQ.