Well, the makeshift setup for the seedlings seems to be working. As of last night, most of the tomato seeds had sprouted and grown to 2-inch seedlings and there were signs of life in at least two of the pepper cells. I also got some additional varieties of tomato and pepper seeds from my boss, but we haven’t sown them yet, but it looks like the seedling tray is going to have some empty cells a lot sooner than we realized.
Of course, we also forgot to turn on the light this morning, so they probably won't do much growing today. (I have an in-wall timer that I bought for the porch light a while ago but couldn't install because of the cira-1940 wiring upstairs; now I'm thinking I'll install it in the basement to protect the seedlings against our morning forgetfulness.)