December 10, 2014 3:04 PM EST
For me, it really depends on the particular skills and how many perks they need.
For example, Sneak can be perfectly viable and useful with just Stealth 1/5, Muffled Movement and Backstab. Speech only needs Speech 1/5 and up to Merchant to be extremely valuable.
Basically the less perks you have to put in each tree, the more skills you can use. Of course, this is balanced out by the fact that having 3-4 perks in certain skills like 1H and Enchanting isn't nearly as helpful.
Personally, the fewest skills I've ever ran with is 4, on my Orc warrior. Just 1H, Block, Heavy Armor and Smithing.
The most? A rogue I ran with some time ago used 1H, Block, Heavy Armor, Smithing, Illusion, Destruction (only elemental buffs), Speech and Lockpicking. It actually felt surprisingly solid.