Has anyone yet tested if a pokemon can get a better CP if you catch it with a high CP and level it, or can it reach the same CP if you feed it candies?
Yes you can increase the CP to be the same on all Pokemon. This will however cost you a lot of stardust and candies. It's generally better to save these items for a few levels so it's cheaper to upgrade pokemon you caught with a higher CP.
The cost of upgrading with stardust also goes up the higher the Pokemon's CP becomes.
The max CP depends of the IV of our mon. More he is close to 100%, the higher he could become. If our mon is 250 CP with 100% IV it could be very interesting to power him up but it will be very expensive. Anyway when you want to power up a mon, base your choice on his IV. But it's cheaper if the mon is already high CP (= lvl)
My personal tests showed the same outcome of candy feeds and high CP catches. Catching a mon with higher CP saves you a lot of candies, but the max CP the mon can reach will be the same. There is no advantage in spending the stardust early, unless you need some extra power to attack an arena.
Save the stardust and don't power up weak mons.