Sounds good..I would say don't use all the same weapons..might get a bit boring..and its nice to individualize your own wep.
As for the role of a sniper in airsoft...yeah thier not killing machines, thier mainly used for scouting and if seriously needed delaying tactics. A airsoft sniper is not marked by skill with his rifle but by his ability to conceal himself..and in my opinion thats the mark of a superiour player. (if you didnt catch it I recomend having a good scout :p )
The reason for a sidearm is not you running out of ammo, it is if your rifle jams, a fuse blows..or your battery goes dead and you forgot your replacement, it allows you to continue play till you can repair your rifle.
The best thing you could do for now is set up a nice chain of command, and get yourself some radios and a throat mike, our affialate site TASS (Link is it the user bar) has some great recomendations for start up gear, heres the link to the page and some good articles to read.
TASSGearPicking a rifle and some further info (geared for sniper rifles, but relavant to AEG's as wellchoosing the right BBThat should do it for now ;p
Good luck with your team!