Formation Suggestion and Auction Question

My current formation is

All Lvl 15 and Skill Level 1
Arachne (B+) w/ Slumbering Breath
Jade Rhinoceros Beetle (A) w/ Increase Party Def
Hell Hammer Spider (A) w/ Decrease Enemy Atk
Poison Spit Frog (B+) w/ Venomous Breath
Cursed Georug (A)

Recently I got a Fire Wing Roc (A+) w/ Increase Party Atk and Dai Tengu (A). I was wondering which monster I should switch out for these two. I was thinking of taking out JRB since I hear defense is not that important and either Arachne or PSF. But I hear Venomous Breath is a good skill if it's high level.

Also how much is a good offer in gold for a A/B+ rank monster? And what do you think an EP is worth in gold?

Lastly, I have a Caim (B+) w/ Agility Up. Is this worth anything and should I put it in my formation instead even though I would lose my guild bonus?

Thank you!

Take out Arachne and frog.
build a team of A+ try strive for a goal.
say i want a rancor A+ beast team for example then you work on acquiring those monsters...I only say beast because that way if you get your hands on bayard you get the agility skill.

Thanks for the suggestion!
I will be building my team towards an A+ ranking.

Anyone can offer any insight into the EP/gold ratio?

EP gold ratio is anywhere from 100k to 250k per EP depending on the market at the time and how desperate the seller is for either. That's about a ballpark number, but I've seen most people around the 200k mark per