Just stay out of the actual mosh pit and just up closer to the actual stage or along the speakers and you'll be fine and anyway the closer you are to the stage the easier it is for security to see you and pull you out if you're gonna faint or get sick or something.
The front's definately more claustrophobic though especially towards the center microphone at cob gigs.Head for the sides,you'll generally get a better view from there anyway.
I've worn glasses to every gig I've went to and never had a problem with it so you should be able to mind your stuff ok. It'd be a bit annoying to have to mind and hang onto a bag during the gig but If you don't mind that it'll be fine
Yeah its just if I dont have a bag I mean; where do I put my merch? I intend on getting a Bodom tour shirt, FTR Flag (if its the FTR ones they are selling) and a CC tee. I cant wear like 3 tee's, and carry a flag, so the bag is neccessary i'm thinking. Unless you have another idea...??