Abra - Kadabra - Alakazam

The answer is simple, don't do anything, just save your candies, I would never mass evolve a mon like abra or kadabra, there is no point, you already have the best attacker and some "middle" prestigers.

I would just save candies, imagine a perfect world in which some day mega evolutions come, you probably will need more than 150 candies to get them/power up. I have a 91%IV PC/PS Alakazam and 130 candies, I won't evolve any other unless I got to the point I have 500 candies or so and don't know what to do with them.

If there is any chance that you want to transfer them to make room in your inventory though, during an extra candy event is when you want to do it. For the extra Kadabras, I would set some sort of higher limit like transfer any that have 12 or less stamina IV.

What %IV is your Alkazam?

If it's a 90%+, I agree that you should probably do nothing. Since it has the best attack moveset, you can just power it up as your level increases. There's no reason to evolve another one unless it's like a 100%IV and you have a ton of candy.

The IV of your Alkazam can also be used to set the ceiling on what IV Abras you actually store, as you wouldn't consider evolving another one fully unless it was of higher IV.