Ventilation For Homebox S

I have a couple questions about setup of my Homebox...

So I have a Homebox S (found here)

buy-the-homebox.com - universal indoor grow box kit

I am planning on putting a 250w cooltube in with its own intake and exhaust then having a separate exhaust going into a carbon filter. It's only going to be a few plants (just doing this for personal use). I guess my real questions are about dimensions and sizes.

These are the dimensions for the holes in the Homebox:
Inlets and Outlets:
roof:


back top:


bottom right:ø 160mm
(6 1/4 in)

ø 90mm
(3 1/2 in)

ø 130mm
(5 in)
Nothing in ventilation world matches these specific sizes, so I was wondering what everyone is using for this setup and how well its working? Since I only have 3 holes. Would going with the Cooltube be useless?

Thanks
Blazor

i would connect the cooltube to the two largest holes with 4" ducting with a decent sized fan as suggested. i'd put an exhaust fan on the smallest hole with a carbon filter attached then i'd crack open the room or cut another hole for a passive intake.