My guess would be that what size octopus clips to try would depend on where you want your part. If you part in the middle, you would try clips small enough to put two across the front of your hair, one on each side of the part. If you part on the side, you might want to get 1 to put across the middle of the front of your hair, and maybe a smaller one to put on the other side of the part, depending on whether you want lift to the side as well. At least, that might give you a starting point. If you pick up a few sizes at the dollar store, it won't be too expensive to buy two or even three sizes to experiment with.
If I use duckbill clips, I was getting "good" results with them going front to back, like I have seen on videos. Used this way, though, they seem to catch in my bangs, and cause frizz, so I am still experimenting with other methods, too. I like using the long duckbills across side to side, but I have bought octopus clips to try, too. It seems to me, that there would be less chance of these catching on and frizzing hair, but only experience will tell.
Experimenting with too many products to name here. All this great info keeps my head spinning.