Hi, I've always been a fan of the Stargate series, bar Universe, so I'm really glad I found this mod...

It's nice to see new faces here

.
Now, about your post:
There's a smoke cloud+small explosion that will appear when a staffweapon hits sth. ("ammo_explosion" or so), but I never saw it building up with each shot.
Yeah the jaffa can be a little odd sometimes. These bullets, are you talking about every weapon even BIS ones or just SG weapons? Certain other mods will kinda interfere with some of the effects the SGMOD uses for weapons, so if your using any other mods I would suggest disabling them and see if that does anything.
Yep, I'm with bait on this one. The message sounds like some other addon is screwing up, never got such an error.
Try disabling all mods except the sgmod addons and start up again. Also for the Jaffa, check your diffuculty settings, advanced tab. If you set the skill values low, Jaffa will miss very often. Better set them to 0.9 - 1.0 if you didn't allready. I once had it set lower and the Jaffa were shooting 1m above my head.
Then I switched to higher values and got a staffblast right into my head.
You can also try moving with large groups of Jaffa, say e.g. 30 Jaffa in one group so they communicate better.