I think a good breakdown of attributes is six of them: Strength, Agility, Fitness, Education, Perception and Confidence. None of these are "intelligence", by the way; there's just how much the character notices, how much they know generally, and how much "stick-to-it-ness" they have.
Skills are a bit harder to figure out a good number for.
In his
Risus Companion - well worth the $10 even if you're not interested in
Risus, just for the GMing and play advice - S John Ross talks about the dozen basic things adventurers do. He breaks them down into,
- Athletics
- Persuading
- Communication & Protocol
- Detection
- Driving, Riding & Piloting
- Gadgeteering
- The Medical Arts
- Wilderness Mastery
- Scholarship
- Intrusion
- Combat
- Magic
If all you have is that dozen, what you've basically got is not skills but character classes: athlete, face-guy, etc. If you want that, great! But if you want some diversity in characters, you need skills rather than character classes. So you need more than a dozen.
What you can do is decide what's important in your game, and split off each area as appropriate. So in a gladiatorial combat game you'd probably have twenty or thirty combat skills, maybe a couple of driving skills, half a dozen athletic skills - but wilderness stuff, scholarship and so on might just be skills all by themselves. Whereas in a game of internal university politics... you get the picture.
Me, I split each into three,
- Athletic: Acrobatics, Climbing, Swimming
- Combat: Brawling, Fire, Melee
- Communication: Languages, Speech, Writing
- Detection: Interview, Search, Tracking
- Driving: Aircraft, Landcraft, Seacraft
- Gadgeteering: Engineering, Handicrafts, Technician
- Intrusion: Burglary, Deceit, Stealth
- Magic/Psi: Body, Elements, Mind
- Medical: Physician, Psychology, Veterinary
- Persuading: Acting, Diplomacy, Intimidation
- Scholarship: Liberal Arts, Law & Society, Sciences
- Wilderness: Hunting, Navigation, Survival
That gives us 36 skills. Some of them vary a bit according to the campaign's technology level - in an iron age campaign, "landcraft" would include horses but not
Star Wars-style speeders, but in a space age one vice versa. In a medieval fantasy campaign you'd effectively have just 33 skills, since the Gadgeteering ones wouldn't be relevant; in a modern realistic-themed campaign, no magic/psi skills.
If only 3 to 6 of the skills are any use at all in your campaign, again they become effectively character classes, so if you want them to remain skills, you'd have to split them out a bit.