RPM vs basic magic

[FeiLin]

I'm currently looking into ritual magic (RM) and am trying to figure out how it differs from the basic system. I should also note that I'm not so experienced with GURPS magic to begin with (perhaps partially because the basic system doesn't feel as intuitive as rm, which is why I wanna try that instead).

First I have a few questions about the cost (to make sure I got that part down). Let's say I have two mages one standard and one rm. They have IQ 14 and magery 4 for a total of 80+45=125 cp. Then they happen to wanna learn the same spells, namely fireball, explosive fireball at skill 16 and 14 respectively, and summon water elemental at 15, but don't care about any other colleges/skills. (They're twins, but have grown up each with a different parent, so their approach is different but their ambitions and situations are eerily alike...)

For the "basic mage", this would simply be ploughing down 3 points in the three fire spells required, and then 12 in fireball and 4 in explosive fireball. The water elemental requires 8 points in water spells (or 3 more fire spells, summon fire elemental, and 4 water) and then another 8 to bring the spell itself up. That costs 19+16=35.

For the "rm mage", this would first cost 16 for thaumatology/ritual magic. Then the fire college also lands on 16, while fireball has -3 in preqs and thus costs 4 and its explosive sibling has -4 and comes in at 3. The water side comes in 12 for the college and 9 to remove the penalty to get the skill up to 15. That totals 16+23+21=60.

I'm not expecting anyone to verify my math, but just to double-check, prerequisite penalities are still in effect for rm even though they're met, right?

I don't know if it's explicitly stated somewhere, but I guess that forbidden schools etc means you can only take a certain forbidden path if it's the only one, and in other cases of multiple paths you can choose which one (i.e. the lower), in rm as well, am I correct?

Does rm have the same limitations regarding colleges (for instance to reduce the cost of magery) or is that built into the whole setup? (Again, sorry if this is stated somewhere, but can't recall it.)

In general, how are the costs and strategies for setting up mages in the various systems different? Based on my calculations above, I'd say that standard more encourages building on branches but slightly more forgiving in mixing between colleges (i.e. you could create your own tree, with branches plucked from different colleges). Rm, on the other hand, makes it slightly easier to pick individual spells within a college, but quite a bit more expensive to add another college. What results has it produced (both from a player and a GM perspective)?

Also, thematically, it would perhaps make more sense to have more generic institutions of magic with rm since it permits defaults, which might generate inspiration in other colleges, while basic more favors specialisation and "branches"?