With pressurized CO2, I'd say that CO2 is unbelievably cheap, so aerate to your heart's desire (and keep fish healthy and happy) while jacking up the CO2 as high as possible.
With DIY CO2, there's no way you'll gas out your fish unless you're really, really trying to. More O2 in the water column is always good for fish, but you won't hurt them by injecting DIY CO2, so I would suggest not trying to create extra surface agitation until you - inevitably - upgrade to pressurized CO2.
Basically, stop worrying. Set up your DIY CO2, change it out every couple weeks, and keep surface agitation to a minimum. It won't be an issue until you have a cylinder and a regulator.