Hello! Newbie here! The name is Khirmell!

I have some questions that needs some answers.

1. I know that I can equip any rank of equipments but it has its downside though. My question regarding the gears is about the rank.

Example:
Sword = optimal rank 15

Should I based it optimal rank to my physical level or PUG rank so that i will not blindly buy equipments that is not yet suited for me.

2. Is about the Quest Leve, why is it I cannot anymore battlecraft leve after I finish them? And another thing about it is that why is it when everytime I get a quest leve the NPC wants me to exchange it with the leves that I finished previously. What is the benefits and purpose of exchanging it?

If anyone could help me answer these question is very much appreciated. Any guilds out there in Palmecia server that can invite me (Khirmella Witwood lvl 14 PUG)?

Thanks again!