1) give as much as you wish...I'd give it much
2) don't know about the DCGUI's import...at least there's no such action in the menus. but check out dcgui.berlios.de for info on if it's compliant with DC++'s filetypes or something.
3) no experience - but if you've got a driver for it, then it almost certainly does work..
4) linux can both read and write to/from fat32 partition. windows, instead, cannot read nor write to/from your linux partition, unless it's fat32 which it shouldn't be
5) the other pcs can access your box, but if they use windozes you should get Samba for the network sharing..if they use linux too, then a nfs might be your tool...
6) you can access the files, if you just set permissions so and get the software for it (for windozes and so on)....and yes, linux can run without problems. I myself have run an old 200mhz pc for over two weeks now without rebooting, and without any kind of performance problems..