Blue Sky vine??

How big should the pot be?

That depends on how big you want it to be. Mine came in a 3gl pot, the vine was managable, then the roots escaped out of the bottom holes and now it is going wild. I have to trim it every few weeks to keep it in control, thus no flowers yet this year.

I've let mine go. I just couldn't keep it within bounds and so little bloom that it wasn't pretty. I planted mine in the ground last year and when I dug it, and that wasn't easy, I think I broke the tap root. It didn't last long, but I took a few cuttings, got one to root, and gave it to my niece. I'm glad she has it. I loved the bloom, but just not enough color for me.

Shirley,

Probably lack of heat, not enough warm time. I have seen them in two places on the way to the office the last two year. One was at a VA building, it grew along the chain-link fence, and the other one was up an arbor at someone's home. They were loaded with blue flowers on and off.
Last year mine has as many as 10 a day during the heat of the summer.

On the West Coast of Mexico the bloom all winter. They cover buildings and arbors and are gorgeous. We barely get to enjoy them here, but my friend in Mississippi gets lots of blooms.

My real estate is too valuable to have just a few blooms on such a large vine. Wish it would have done better because I loved the blooms and the foliage was nice too. Just traded it for Mandevillas this year. Plus, I have some very nice Passifloras.