A few things I noticed.

Adding levels to levellist.ini by dragging to plus.exe works, but only for small numbers of levels. I tried adding several hundred at once and it gave an error.

If there is a missing entry in levellist.ini, like this:

064=blah.j2l
066=blah2.j2l

and you try to go /levellist sort, it will only sort up to level 64. After that it will keep the list the same as it is. Sorting should probably arrange the list so that blank entries are removed.

When hosting, I noticed that minimizing jj2 cuts cpu more than the shift+f2 method. I also noticed that lowering the resolution and minimizing basically cuts cpu to 2% or so. It would be nice if some sort of special hosting option could be implemented so the game constantly runs at that cpu level (or less). This can be done by having the game not render graphics, or setting the resolution to something like 1x1 if that's possible. It would be like a ghetto dedicated server: still uses the jj2 exe, but the host itself is unable to play. Obviously input would have to be handled through some other means, such as an improved chatlogger.

The reason I suggest this is mostly to have a hosting option that is as resource light as possible.