I just shot a convention with a GX1 so I'll share a few of my thoughts :). Forgive the semi-coherent ramblings!
On the topic of white balance, I find that the GX1 does very well. Don't be afraid to use the custom white balance(s); the GX1 does it quite well and since it has a devoted button it's quick enough to swap between them. The convention center I was at was all naturally lit (where Auto WB does well) aside from the programming rooms, though, so it didn't come up too much for me.
I always shoot RAW+JPG. For starters, IIRC Panasonic uses lower quality previews if you shoot RAW only. Mostly, though, it's convenient to have JPGs for images you don't want/need to process the from. For a convention, this will likely be most of your pictures, but it's really nice to have the RAW around for those that need it for one reason or another. If you are worried about space, a $20 32GB card will hold plenty. Particularly if you use a little downtime to delete obviously failed shots.
On the topic of flash and lighting... Lighting is going to be an issue of course. I don't really like flash in general and find it only of limited use in a convention setting. Usually you're facing larger spaces than the built-in can well illuminate so it can be tricky to get good shots. It depends on the situation, of course, but it can be all too easy to, say, get a person well lit against a near-black background where the rest of the convention should be.
Auto ISO can be quite nice because it makes it harder to leave it on the wrong ISO when you switch locations as you probably often will ;). However, it doesn't quite keep the shutter speed up (usually dropping ISO at 1/100 or so) so you may want to just manually set it to ISO 400 or 800. One important thing to remember is that while lower ISOs collect more light and thus have less noise overall, higher ISOs (up to 800 or 1600) have lower noise in the shadows. In a convention setting where you'll probably be looking for better detail in the darker areas, minimal ISO is actually going to work against you in some places.
Lens wise, I found the Panasonic 20mm f/1.7 to be indispensable. It's a great focal length for being able to grab full body photos (useful for costumes) at close-ish range, which is important when loads of people are walking around. It's also wide enough that you can get a lot of the environment in the frame (it's no ultra wide angle, but neither is 14mm, IMO, so I don't care that much). I have the Sigma 30mm as well and find it a little long as you do.
Most importantly, though, it's fast. I don't like to shoot the GX1 above ISO800 and at that ISO and f/1.7 I was barely freezing subject motion in many settings. If you are limited to f/2.8, expect that you'll need to push your ISO to 1600 often and even then face some frustration. It will likely be compounded by the lack of any stabilization and longer focal length. That said, I do like to take somewhat more candid/active shots, so if you are more interested in people posing you can probably manage better. (As an aside, some folks say the 20mm focuses too slowly, but I never had an issue.)
The 45mm f/1.8 ultimately didn't end up working well. It was too narrow to catch ambiance and full body shots were hard as well. With the 20mm I could say 'can I take you picture' and step back; with the 45mm it felt like I was running away from them ;). While I probably could have made more use of it shooting aforementioned candid shots, it wasn't really appealing enough for me to take off the 20mm... Partially because I'd have to get pretty far removed from any activity to ensure I wasn't cutting anything out for nearby shots and I'd still have to crop for more distant ones.
As far as the zooms, yes, they won't be forgiving in convention lighting. You can get good shots, but don't expect a lot of keepers. (This is generally more subject motion than shake, but obviously that depends on focal length and how still you can hold it vs the stabilization.) My 14-42mm G X PZ stayed in the bag unless I needed it for video. It was ultimately just too slow and it's easy enough to take a few steps to reframe the 20mm that it didn't make sense. I did, however, reach for the 45-175mm G X PZ quite a few times. While slow too, it's hard to pass the 8x of magnification over the 20mm!
For your lenses, I would say to not discount the 45-150mm for indoors. It's slow and you'll have a low rate of keepers, but you'll also be able to get some shots you couldn't otherwise. Sometimes it's neat to be able to catch the action on the other side of a large room. Also, I can see the wider end of your 14-42mm being useful since you don't otherwise have anything wide (even if you don't usually shoot it that way). The low light won't punish you all that badly in that case, as you'd be under f/4.0 and thus barely a full stop slower than your 30mm.
Finally, the zooms will also be quite handy if you plan on shooting video. The OIS should be competent enough to let you do okay hand held (the Power OIS in my X lenses was quite excellent, your Mega OIS lenses will suffice though). Also, the ability to zoom can be quite handy. As a couple quick notes, ensure that you pick a seat that gives you good zoom flexibility... That is, ensure that at the widest you can see beyond the edges of the stage so that you have room to zoom in on action if you want. Also, the GX1 limits video to ~30min in MP4 format. So if you prefer that mode note that the time remaining is (probably) not the memory remaining and that you'll want to split the video at sane points rather than having the camera cut it for you. AVCHD format offers unlimited record time (US only), but I don't care for it as much.
Accessory wise, a second battery is, of course, useful. I can't really say if I would have gone through one in a day because I would switch halfway through as a precaution. Still, I expect it's possible to get by with one; it depends on shooting. If you have an LVF2 it's useful for shooting in dark rooms (i.e. in the audience) without annoying people if such a thing might come up (not sure about DragonCon). I forgot mine and only kicked myself once though.
So that's about all I can of (my that got long). I would recommend you look into getting a Pan 20mm f/1.7: they are quite cheap right now on eBay due to the announcement of the metal version and very much worth it. Other than that, make sure to remember to set the camera down and have enjoy the con on occasion ;).