Good idea to disable the mods - you dont want to get kicked out for "has hacked table data" messages

Just remember the basic rules and all newbies should have a good time:
1.) Always stay on low object updates when you join a game as a client (F2 key > multi settings) Most think because they got a good con that isn't mandatory, but it really is: If one client pulls to much data, he lags the host and the host lags all the other clients - a sure and fast way to find out that the host sees the transfer rates and owns the kick button

2.) Never haste a host. No "go go go" "when do we start here?" Usually waiting time is spent to get more players in a game and/or to keep a game open for some time so friends can join.
3.) Stay polite - that works wonders

4.) Don't click or type in the debriefing screen until it says stats saved - PXO seems sensible and sometimes drops the process if you don't.
5.) Make sure you installed the missionpacks (I also recommend the additional voicefiles) from the BDHR site (see my sig) - nothing is more annoying then waiting for a mission transfer. Btw the few mods on the same site work in multiplayer without getting the hacked data message.
The online community got a lot less hostile to newbies since squadwar only works at random times (if at all). Most players are around on the weekends - and you certainly will find games to your liking (TvTs, Coops, Dogfights). If you stumble into TvT players that shoot you all the time, don't get frustrated you can just leave and find yourself some Coop players who are always around too. The main difference between single- and multiplayer FS2 is that you need to get used to forward aiming because your ping isn't zero when you are the client.

Last: Have Fun!