How many Vaporeon is too many?

It's probably worth keeping a couple of low cp for gym prestiging. I've got a lot of stuff I could transfer, but the thought of just a single candy makes me hang on.

And I've widdled them down considerably, used to have much more, when taking down a few level 10 gyms and running out of potions was a thing. I've never used more than two of them in an attack or had much more than 5 of them in gyms.

Obviously we all have different preferences and rules and whatnot for our 'collections' but like you I previously had 15+.

Now I've transferred all but 5. I decided to keep only the 90+ IVs and two of each offensive preferred movesets and one defensive.

And I tell you man, I felt SO much better after getting rid of them all that I basically cut a ton of the fat in my collection. I have my strict rules now and I don't budge on them at all.

This

Vaporeon is a good trainer for friendly gyms. I keep like 20 of them CP 1000-2000 plus 1 2700cp for attack and 2 2900 for defense.

8.75–17.5 is perfect, over 35 is too many, over 70 please transfer at least half of them.

Depends on your level, transfer CP below 1500 and have bad IVs (below 1750) away.

Considering it's probably the most useful all around Pokemon I'd say using 5% of your bag space on them is reasonable. If I were to venture a guess, you involve them in at least 5% of gym battles...probably considerably more.

The only time I find a deep bench coming in handy is when I'm running low on lower potions/revives and am rolling through a handful of gyms in a row

I have 27 Vaporeans.
CP 43-2999.
Best Pokémon to train/attack gyms.
Easy to dodge, Huge HP, powerful water Pokémon.
My GO TO fav.
Only transfer identical/very close CP.

Or you could hang on to them for trading to guys like me with 15 Flareons, 12 Jolteons, and only 3 Vaps Rumor is that is happening in December.