Honestly, any more than like 2 or 3 is excessive. Focus on tuning and improving the decks you have; you'll get more out of them that way. Don't spread your card pool too thin; a lot of builders do this and end up with 8 pile-of-trash commander decks instead of making 1 or 2 solid ones. Then they whine about losing and I'm like, ???? Do you not realize why you keep losing??
It requires more effort and costs more money to maintain a large stable of decks, but that doesn't mean that having a lot of decks means you'll have a bad card pool. I have a good income, and so I don't impose any particular budget on my decks. All my colored decks have shocks and fetches, and a few have Revised duals, as well. My Karn deck has Workshop. Etc.
There are currently 690 legendary creatures legal for commander. So 691 is too many.
magiccards.info says 680 while Gatherer says 700, and both of those searches are including the 15 nonlegendary Kamigawa creatures that flip to become legendary (Gatherer includes both sides in the search results, for some reason, while magiccards.info only includes the legendary side). Neither search is including the 5 planeswalker-commanders, either.
I'm working towards one deck in each color combination (5x mono-color, 10x dual-color, 10x tri-color, 5x 4-color, 1x 5-color, 1x colorless, 32 total). I'm currently only missing Bant, Esper, 4C nonblack, and 4C nonred, and I'm working on designing my Esper list.
Once I finish with my 32, I've got some ideas for new decks in a color identity I've already got that are different from what I have. For example, my Grixis deck is Thraximundar stax, but I also kinda want Mishra uncounterable artifacts. My mono-color decks form a cycle of commanders that each cost 1MM and have base P/T of 2/2, but a while ago I got the idea for getting some Scooby Doo alters -- Isamaru as Scooby, Batterskull as the Mystery Machine, Stonehewer Giant as Fred, Sword of X and Y as various flavors of Scooby Snack™, etc.
(Also: two decks with Snow-Covered Plains)
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)
Once I finish with my 32, I've got some ideas for new decks in a color identity I've already got that are different from what I have. For example, my Grixis deck is Thraximundar stax, but I also kinda want Mishra uncounterable artifacts. My mono-color decks form a cycle of commanders that each cost 1MM and have base P/T of 2/2, but a while ago I got the idea for getting some Scooby Doo alters -- Isamaru as Scooby, Batterskull as the Mystery Machine, Stonehewer Giant as Fred, Sword of X and Y as various flavors of Scooby Snack™, etc.
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)