Challenging indoor shoot

I spent last night working on another assignment from my church. We have a dinner before church every Wednesday night and they wanted some photographs for the website. My challenge was to find a shot that tells the story of Wednesday night dinner on its own, as they will probably only use 1 or 2 of the photographs on the website. The other challenge was the lighting. One half of the dining hall has a huge stained glass wall making for challenging WB conditions but provides enough light at sunset to shoot at 400 ISO. The other half of the hall (where most of the people are) is very dark and 1600 ISO barely pulls the shots out. Even when it does, the noise level is very high. All I have right now is the onboard flash, but even with an external flash I can't see it filling any significant portion of this dining hall. I used my kit lens for this shoot which is f/3.5 on the fast end.
So, what should I do? I can try to get closeups of people with the flash, and see if they can live with the dark background. I can try to only take photographs on the bright side of the dining hall and adjust the white balance in the post processing. I can also try to save up and get the f/1.8 50mm lens that only costs about $75. With the increased speed of this lens I might be able to get the shots on the darker side of the dining hall at a lower ISO. The only problem with that solution is I am not sure it will work. One other idea that I almost forgot about is to shoot these photographs in the second dining hall. I never eat down there, so I forgot they serve dinner in two different places, and the second one has much better lighting.
I am going to get some samples of the ones I took last night to the people requesting them so they can give me some ideas on composition. Hopefully I get the shots they are looking for next week.

Headshots

I am helping my church as the assistant photographer. My first assignment was to shoot some headshots of various people for the website. These are not typical thumbnail shots as they wanted high detail photographs they could manipulate and use as the page header for each respective ministry. To say this was a learning experience is an understatement. I spent some time on the day before practicing on my daughter in the living room. Lighting was the big challenge. I don't have an external flash and I hate the harsh appearance I get when using the onboard flash for portraits. I used a coffee filter to diffuse the light which worked fairly well in my living room. Unfortunately, this did not work nearly as well at the church even though the background was almost identical. The shots came out very dark even though they looked properly exposed on the LCD and the histograms looked OK (EDIT - A second look at the histograms shows they do NOT look OK. I can see a large spike in the middle and a smaller spike on the left with nothing on the right. Clearly underexposed. This is something I need to remember when I set up my practice shots next time.) All I can say is thank heavens for RAW. I was easily able to correct the brightness level and the Canon software did a good job of balancing the skin colors.
Besides purchasing an external flash (which I cannot afford right now), I am not sure what I would do different next time. I definitely would shoot RAW+JPG for important items like this. That was a life saver. I might overexpose by at least +1 and maybe even +2 next time if I used the diffuser. I don't want to go to far as it is easier to pull detail out of a dark photo. If I overexpose too much and blow out the highlights, there is no saving the detail from that.
I am also deliberating on whether I made the best lens choice. My kit lens is faster than my zoom, so I might get better results from the lighting. I try to avoid shooting with the kit lens at 55mm as I think images are a little soft (I have not done tests to prove this though). Benefits to using this lens would be that it lets in more light and the flash would have been closer to the subject. Drawbacks would be somewhat less depth of field than using the 75-300. I need to think about this some more. It might be time to make the homemade softboxes from the photography lessons on www.morguefile.com and use those instead.