1.-what's the minimum PL required to moon bust?
139 as Master Roshi was able to blow up the Moon
2.- what's the minimum PL required to planet bust?
18,000 As Vegeta blow up a Planet during a filler episode.
3.- are those PL proportional to the size of the object? (earth is 50 times bigger, you would need 50 times more PL according to logic)
4.- going by a proportional scale: is Frieza a solar system buster? if you think so answer the next question, if not skip.
Yes. As far as we know Frieza blew up 2 Planets Namek and Vegeta. He could easily blow up a Solar System if he wasn't fighting someone like Goku or the rest of the Z Fighters for like 20 episodes long. I mean anyone would be tired realistically even by anime standards if they aren't dead already. He held back as he was afraid that he wouldn't be able to survive the explosion with enough time to escape.
5.-why frieza couldnt one shot namek when the required power level to destroy earth is no more than 10,000?
See Question 4.
6.- is namek 100 times bigger than earth? even if frieza held back according to his PL he should have blown it to nothing even with the 1% of his PL. explain this fallacy.
See Question 4
9.- why can krilin at a PL of 75,000 can cut frieza at a PL of 120,000,000?
Frieza wasn't paying attention when Krillin cut off his tail so he didn't have time to surround his body with Spirit Energy in order to protect himself. When Gohan caught Cells attack he was using Spirit Energy to slow it down enough in order to catch it.
10.- how does PL take into account special abilities like time stop, breathing in space,lifting strenght,speed,DC, and h2h skills?
It doesn't however Goku was able to Stop Trunk's Sword attack by concentrating his Chi into his finger. Bleach which is very similar in terms of abilities and Special Powers explains that they are able to use there Spirit Energy to increase there Punches/Sword Strikes and ability to survive falls that would kill anyone else by Surrounding there bodys with Spirit Energy.
Although Goku was able to use Telepathy after training in 100 times earth's normal gravity which he never had the ability before.
11.- why should power levels be used instead of feats? (goku defeating frieza makes him a planet buster. but why should it make him multi solar system level?) elaborate.
Akiria basically abandoned Power Levels after the Saiyan saga.