I agree with this - not just too big for the plants in their early stages, too big for coir, unless you have a very specific plan minimize watering requirements, in which case soil would probably make more sense. I use an aero cloner, so I only use Solo cups when starting seeds, then into 2 liter pots then into the 2 gallon pots where they finish. 5 gallon pots with coir are for LARGE plants , like plants that would be too big for one to fit in your tent. I'd probably finish this run with what you've got, but I'll bet when you break things down, you'll find a root ball that would fit in a 1 or 2 gallon pot.
Also wanted to mention that your plants shouldn't start to stink until they get bigger. If you're trying to budget purchases, you could probably install the duct fan and ducting first, then add the charcoal filter in a few weeks.
