The cantrip/spell/ritual offers a lot of flexibility in giving each spellcasting class a different "feel". Wizards may be the default, with limited slots and ritual casting. Clerics may also have access to rituals, but cast spells spontaneously from their domain list. Sorcerer may have no access to rituals at all (they would have to take a feat), while bards use rituals and cantrips, but no spells.
We're in the same neighborhood.
Wizards, as academic casters, would have access to cantrips, spells & rituals, but would be limited in amounts cast per day in typical Vancian style. They would, however, have access to a wider variety of known magics, and could alter their arsenal with a bit of study time, and could always expand their list.
Clerics- also studious, but not in the same way as Wizards- would also have access to orisons, spells, & rituals, but their lists of would be rigidly defined by their faith. Learning magic outside of those lists would be done via a "Forbidden Knowledge" Feat.
Sorcerers and other "intuitive" or "innate" casters would know cantrips & spells, but soul have to burn feats to learn any rituals. Their cantrip/orison use might even be unlimited at-wills.
Bards- you nailed.
Lesser casters whose powers come from some kind of pact with extraplanar beings- Warlocks, Paladins, etc.- would have a rigidly defined lists of cantrips/orisons and spells. Their access to rituals would be class-dependent. Warlocks might start off with one or two. Paladins* might not know any to start, and would be restricted on what kinds they could learn- healing rituals OK, undead creation, probably not.
In cantrips, I'd avoid giving bonuses, and even rolls. They should be as simple to use as possible.
Continuing the Knock example, I'd make the cantrip version automatically open locks to a fixed difficulty (eg. what a equal-level, average-dexterity rogue gets by taking 10) and fail against harder ones. This way, a wizard is never stopped by a poor lock, but a rogue is a little better in every case, and is able to defeat high quality locks that the cantrip can't even touch.
I still think the cantrip version of Knock should be limited to giving a bonus to someone with skill, but I could see a solid argument for it working your way.
* or, if the game has "Holy Warriors" instead of Paladins, their list would be definede by their faith- resembling a watered-down version of what their clerics have.