What other store worlds do you have? Hidden Springs and Roaring Heights are two of my favorite worlds. If you're not opposed to downloading content at mod the sims they have both Sunset Valley and Riverview and I think Bridgeport cleared of all buildings and Sims. You could do the nothing is free challenge mixed with the legacy challenge. It will at least give you a set of goals for each generation. If you choose Riverview then perhaps set it up so that your sims are generational farmers. If you have the cows and chickens from the store it adds a nice touch to the farm.
In general I find legacies boring. If you want to grind through the generations then go for it. If not I would suggest adding goals(like you would in the NIF, rags to riches challenges) for each generation. I also usually move my elders to a home in the world and let story progression do its thing. Give your starting sim(s) a background story and when you assign traits have them so they react to certain situations according to those traits. Assign your sims aspirations, traits, and careers you haven't used before.
I would really try to break away from the Sunset/Riverview play and try a different town. Twinbrook is a good little town. Bridgeport is fun. If you want to start out as poor couple trying to make it in life they could start out in an apartment and then move into a nice home in the hills.
