as far as your venting goes... your closet is only 70 cu ft...so 172 cfm is plenty. You might need a secondary fan for the intake... to bring a 172cfm of fresh air into the closet/tent it is. So the pressures are equal.

I don't really understand how the cooltube works. Why do you need to duct the cooltube? so the supply air is cold?

for the exhaust part it should be...

duct>filter>exhaust

but im guessing your way could work too...