Some newbie questions( skill de leveling costs/choices etc.)

[Arbitrator]

Greetings.

How much would it cost to de level a specific skill tree level eg. Heuksal from 15-20 to 7 (with no 7-20 skills added, just the raw skill point.) I was wondering if we could level to 25+, in this case with a 5 level gap (20 in heuksal) and deleveling both the skill to 7, and your level to 16. Would this cost a lot? having 30 str would definitely help a lot in sp farming (perhaps ohko-ing a bandit archer with one swing?/one arrow?)

Secondly, is it advisable to neglect the "annihilating blade, fanning spear and heuksal spear series), since we have ghost, soul, combo and flying dragon to cover them up ( Since these three skills look like weaker versions of flying dragon and ghost spear).

Lastly, It is even possible to sp farm with a glaive (pretty tired of bows). Maybe by leveling with a 6-9 level gap until 30+?

Thanks, your comments are much appreciated.