If I wanted to add eggplant, what size chunks and time frame should I use? Do you think it would be a good idea?

Eggplant shrinks quite a bit so keep the chunks on the large side (1" cubes?) if you want to notice it as a distinct component to your dish. I agree with browning the eggplant ahead of time too, it will help flavour and texture.

Hoping Merrill see's this and weighs in but what I would do is either oven roast or saute the eggplant, browning it and add to the sauce in the last 5 or 10 minutes of cooking. I make an Iranian tomato based stew with lamb and eggplant and thats the way I do it and it's wonderful. I love the idea of adding eggplant.