Ok, seems there is not even one topic to found anywhere on a good server.cfg for Dark Messiah as dedicated server so here im trying to start a topic and i hope people can contribute what they have.

Basically what i dont understand is the different gameplay modes and why it's not possible to mix them.

Right now im using this as startup line:
e:\darkmessiah\srcds.exe -console +map L_MP3 +maxplayers 24 +ip OURIP +port 27015 +servercfgfile server.cfg

As server.cfg i have the following options set:
hostname "Our hostname bla bla"

// rcon passsword
rcon_password "thepass"

mp_timelimit 35
team_kill_punish 1
mp_forcerespawn 1
mp_gametype 3

sv_lan 0
sv_contact our emailadress

Can anybody tell now what other cvars should be set if these are good and if its possible to use a combination of maps instea of only l_mpX?

Any map can be used for TDM and DM pretty much flawlessly. You can use the mapcycle.txt file for arranging the map cycle.