The main rule book is somewhat contradictory here. In the Extremely Complex Character Generation insert, they do say that it tends to produce characters who are close to those generated with the detailed rules.
But I don't think anyone here on the forums has said that playing characters through several years is like generating them to the same number of years.
Yes, they can. Victor has some abilities he may never use again. Again, I don't have an issue with extra XPs to add flavor as you suggest, and you still haven't really described the House minima abilities. If you want to provide 450 experience points, IMO, you can't just grant 450 experience points without putting qualifications on how they may be used, if the intent is to create more interesting, broader characters.
What constitutes barely competent? IMO, barely competent would be a score of 1, or 0 with some xp, IMO. Since it's a knowledge ability, it can't be used if there isn't some experience in it. I would venture that a lot of magi have 1 or 0 Code of Hermes, just enough to get by. So the gauntleted Quaesitor might have a score of 3, maybe 4, but I think 3 is a reasonable start for a new character, certainly not a five. Same with Faerie Magic, another House Minima you suggested having it at 5? But why? No one else in the Order really has it unless they are part of the House, so what differentiates a new Merinita from a 10 year PG Merinita? Not a lot, since the cost of going higher than 5 is nearly half of what it took to get to 5.
I guess what using House Minima would really do is make everyone within the House be much more similar to everyone else in the same House, while differentiating them from the Houses of the Order, generally. I'm not sure that's a good idea.