Kyogre Power Up Question

I'd put the rest of your Kyogre candy to #1. After that: wait until your next situation where you need a bigger Kyogre, then use some rare candy--look at a breakpoint calc for that future matchup

5 is strictly worse than 2, tms should not influence your decision. It's 2 or 4 depending on how you value the attack stat. Check the breakpoints. If there is one that you don't reach by having 13a at lvl 30 then take 4, in any other case no.2. Max out your first then.

I personally like having one of each legendary maxed out, even though it’s expensive and the return on investment isn’t that great. It depends on your goals for the game.

One reasonable strategy would be to take the 2300 to level 30 with the candy you have (if you get HP from the ctm), then work on maxing the 98% one as a long term project.

Even if he gets Thunder, you can probably assume you’ll get more ctm’s eventually...

First, do you need do boost yout water squad now? It's irrelevant for Regice but useful against several T3 and T4 raid bosses (if Gamepress' list is up-to-date), so it depends on what you need. You may also want to take your local gym meta into consideration.

If you don't need a boost now (you already have a good one, plus good water mons are common), just wait a bit. Save this decision for when we really need good water attackers, like against Regirock. By then, maybe you will have collected more CTMs and you'll be glad to be able to power your Kyogre #2 or #4. While I'm at it, I'll vote for #4 because it has 15A and may be able to reach breakpoints your #1 won't, while your #1 will stay the most tanky of all your Kyogres anyway. That way each one of your 2 powered up Kyogres will have its unique role ;)

Now suppose you need mote water power right now. If you really can't do what you are trying to achieve with your current forces and a Kyogre could make the difference, if you used all your CTMs and didn't get hydro pump on the Kyogre of your choice, then and only then you could power up your #5. It's not a bad Kyogre at all and although not optimal, the investment will not be useless. Simply consider what this Kyogre could reward you that you couldn't get otherwise and what you could lose by failing another raid or falling short of premiere balls on occasion in the future. It's up to you to see if the immediate benefit is worth it.

Another vanity factor I considered when I first maxed my Kyogre, it will be your highest CP pokemon (excluding Slaking...which is why I evolved a 3280 one of those). Made it a whole lot easier for me to grind those rare candy out since I would see it everyday at the top.