If you're running in a LAN environment then you're unlikely to need say an admin mod, but maybe just get ulx incase you want to force change the map or something. No major settings needed to be changed to be honest, it depends on what you like you can run haste mode to make things a bit more tense (again thinking LAN setting) and various other things can be tweaked it's really what you like.
There are loads of maps that get lots of attention such as 67th way but again it's mostly matter of opinion and as such i wouldn't know what to recommend. I host a bunch of maps over @ http://www.thehiddennation.com/maplistttt
these update when the SNG servers update.
Jihad Bomb and various things like that are custom coded by people, although jihad is likely very easy to find and use most others will probably be broken with a tiny problem that's typically easy to fix. But i don't have a stored up area of any of these (i probably should but you know without making myself not many will just give me code for cool sweps).
Same again for any kind of "prop shop" or mask shop, hat shot, trail shop whatever kind of shop someone has implemented all custom by the server owners. Some might be publicly available some might not but this is a matter of tireless searching more so then anything else, you can find a bunch of stuff working or not over @ http://www.garrysmod.org
as i said not everything will be working/ very good.