Is it right that there are Permanent Booster Locations that Incrase Stats and Resi to 50 if they are under 50? Are there also Boosters that increase to 100 if they are under 100?

Technically no.

However, in MM5, there is, late in the game, a spot where any stats that are below 50 will be increased *by* 50 (note that this is *by* 50, not *to* 50, so a score of 48 will become 98, for example). The catch is, however, that it's in an area that you can't access unless you actually play through most of the game; you can't go there early.

Worth noting that it also ages you 50 years, but at that point, it's easy to reverse it, plus I don't know if it's possible to reach 250 personality without equipment, a shrine, or the bonus from old age.

There's a spot early in MM5 that boosts intelligence by 25 if under 50, but it can only be used by sorcerers. (Haven't tried archer, but I know ranger doesn't work here.)

There's also a place to boost those resistances by 50 if under 50, but the catch is that energy and magic resistance can't be boosted that way, and energy resistance is important both if you want to do the castle alamar dungeon early and if you want to fight the Mega Dragon.