I was thinking I ought to update some old classes I once proposed to the new approach as an example of how to use it. I figured I'd start with the sage.
Concept: Know-it-all without inherent magical powers. This is an example of a Magical+Support combo.
XP/HD: As Magic-User.
Spells: None by default, but can research Magic-User spells and create scrolls of any spell known. Ink Ingredients: taken from a creature with 1 HD per spell level.
Other Abilities: Decipher maps or read magical scrolls as a Thief, even at first level, and use any magic item that involves writing; detect secret doors as an Elf. A Sage has a chance to recognize an item or location as magical (5+ on 1d6,) but only if the enchantment is old and thus possibly legendary; they do not actually cast Detect Magic, but instead remember having read about that legendary item or location. They will also remember specific rumored magical effects with a spell level less than half the Sage's level. At the GM's discretion, a Sage can also gather lore about a specific location (one dungeon sub-level, one surface-level structure) and assemble a book (costs same as a replacement spell book, use dungeon level as spell level.) While the book is in the Sage's possession, one turn of on-the-spot research will answer one yes-or-no question about the location (5+ on 1d6.)
Sages can also learn one extra language per level, beyond the limit imposed by their Intelligence score.
Breakdown: Since Sages are a Magical+Support combo, they use the highest experience and lowest hit dice of the two core classes (Magic-User and Thief.) We drop the Thief's stealth abilities, re-theme the clever abilities to fit the concept, and replace backstab damage with extra languages. We give them spells in scroll form only, but we could have gone with a half-power spell-caster instead.
This may be a challenging class to play, especially if your games are all about fighting monsters. However, if you're playing in a very old-school manner, a Sage can do anything that any other adventurer could do, including figuring out clever non-combat solutions. If the GM includes maps and scatters lots of scrolls around, Sages can be very useful. Certainly, their limited Detect Magic/Identify skill may allow some magic items to be used immediately, instead of waiting to get back to town.