I'm concerned that I have little or no biological filtration with just the socks.
I'm new to the planted tank and am not as knowledgeable as I am with SW.
You wouldn't be the same Dave from RAG would you?
Yes, unlike some of the others, I do prefer some additional biological filtration in the canister, provided you have space in it for the media.
As for a sump or Eheim wet/dry, yes both of these will give a lot more gas exchange and remove CO2 much more than a normal canister. IMO, if your using a DIY CO2 system, or a yeast based CO2 generator, this could be a problem. If you have a high pressure CO2 tank and regulator and so on, it's more a question of turning up the CO2 supply.
Yes, I'd agree that two Eheim 2217's would be better, as far as not loosing CO2. However, these are Eheim classic filters, which means there are no media baskets and such built in. Of course, you could use media bags for carbon and such, but it's still a lot more work to clean.
Your also going to need to buy those, and at a price of about $160 each. $320 buys a lot of CO2.
I'd say go with what you have, and see how you make out. You can always spend more money on the filtration system later, if you have to.
Yes, I'm the same DaveK on RAG. I got involved here because I want to take my planted tank from ok, to something really great. I've learned quite a few things, and am slowly redoing it.