I'm tinkering/looking at it through the other end: Almost everything advances as an Ability.
For Hermetics, there's a fair bit to adjust there - the Form Bonus should become 1/2 the Form, not 1/5; each spell magnitude should be 3 levels instead of 5(level 5 is now level 3, 2 magnitudes down becomes level 2, and two more magnitudes down stays level 1); AL and Phl need to be halved before adding to ceremonial totals; and so on. I've also added Technique Bonuses. They default to helping with Finesse, but if the magus has a supernatural or arcane ability then they can claim the highest applicable Technique bonus: Intellego for Animal Ken, Muto for Shape-shifter, Rego for Entrancement, etc.
In addition there are "spell-like" Abilities, almost always legacies of pre-OoH practices, that can take advantage of both the most applicable Form and Technique bonuses. Many Flambeau have a general-ish Fire Ability that is said to have been passed down from the Founder himself.
Spell mastery is the one place where Ability costs can vary - it's much easier to gain mastery in low-magnitude spells than higher-magnitude spells.
In addition, the Tractati Bootstrap Correspondence Circle does not work, although getting the rules for that to work is looking more and more like a complete overhaul of the book system. This is so that there's good reason for the post-Founder generation to start the rumors that Hermetic Magic can never equal the wonders that the Founders could perform.
For non-Hermetics, it's a little more complicated and a little simpler. Magic is almost always done as a single Ability + Attribute + bonuses, and when it isn't it's because there's a "spell mastery" option available. A lot of things are formulas/recipes that can be learned by anyone with the appropriate Ability, like the stuff in Arte and Academe. Likewise, also referencing Arte and Academe(and ROP:M), quite a bit of stuff just requires the right Academic Ability(ies) to do. Some things are simply Arcane Abilities, and anyone who can work with fluid vis can do them (including mortals who know power-raising rituals). Some things are Spirit Abilities (including a lot of canon Supernatural Abilities) and anyone with a spirit could learn them under the right - albeit quite often dangerous - circumstances. Other things require an Opening to give the framework for the tradition to work.
I should also note that scholarly circles tend to places higher prestige on things that don't have any obvious result(or at least not in the short term), and look down on anything that smacks of empiricus work. The Order tends to react with varying degrees of amusement and contempt when they encounter this attitude. On the other hand, using non-Hermetic Arcane Abilities generally doesn't count as "acting as a court wizard" in a lot of peripheral rulings, even though Technique bonuses almost always make the magus better at it. This is because mortals are used to having such hedgery on call anyway, and depriving them of that (by grabbing all the Gifted children) can be seen as interference in mortal affairs. The Quesitores generally hate these rulings, but direct patronage is actually often a more discreet way to get along with the mundanes - no footprint as independent land-owners, for one - provided the mundanes don't realize just how much the magi hold back on what they can do.