With Regards To The Offline Music QuestionAs far as I can tell, after playing around with it a little, Deepbot's music player cannot load offline media. The music player itself, as you've probably noticed, makes use of Youtube videos in order to deliver files requested by your viewers for their musical enjoyment (or, unavoidably, linking a screamer which they'll hear the sound of, not see the footage). Deepbot itself has a !song command which users can use which will display the current song you are playing if using the Youtube player, iTunes or Spotify (not related to your question, I know, but worth mentioning).
The only other way to do it would be to use a media player like VLC. In VLC you can load your offline music and then when a user requests music via a Youtube link manually putting it into your VLC playlist. Of course this is a lot of effort on your part but currently that is the only way I believe you can do it, sorry.
As far as the file that is used for playlists in Deepbot, the file extension is .PLST. The file contents are as follows (I requested this song
https://www.youtube.com/watch?v=KYfK61zxads)
letest.plst,1,0
1,KYfK61zxads,104,dante557,Best VGM 1552 - Angry Video Game Nerd Adventures - Assholevania
Ignoring the top line;
Position in Playlist, Youtube ID (random characters after v=), Length, Person who requested, Title of video
This file can be edited with notepad if you so wish but as it's not a widely used file for playlists (The stan.dards being .mu3 or.pls) you probably won't be able to open it in a media player you own
With Regards to Welcome MessagesIf you have this enabled it will activate every time a user joins the channel, even if they leave. This is because IRC will send JOIN messages when they decide to enter the chat room. There is no way to stop this with the functionality activated but if you want it to activate when specific users enter then channel, like mods or VIPs for example, you can click on the dropdown box and select what user groups you want to welcome
With Regards to Logging Into Non-Forum PagesIf I can gather what you mean, the forum and the wiki (The other place you can create an account) use separate databases. The main website as well uses a separate database as well but currently there is no reason to have an account on there.
Hope that helps,
Dante557