I'd go with straight sides. (ie: the FIRST table Dave showed)
I've seen many double-pedestal oval type tables like that, and they look great. In my head, it seems like the true ellipse type table Dave showed -- the 2nd one with continuous curves -- would look rather odd with these suddenly straight leaves in them. You'd need to mock it up in Sketchup first, I think, but when I picture it, it just looks weird. I think you're going to get a bit of sharp angle where you transition from the curve to the leaf.
Now as to the construction... I've seen various companies that sell the pedestals, and even sell the complete base as a kit, such that you just need to build the top. Just thought I'd mention that, in case you didn't know. It gives you options to skip some of the parts that you might find tedious/difficult.
best,
...art