FP:
I do not think to start off without C02 means ones is doomed to plant failure. Not even close. You just have to see how the plants develop as lightiing and substrate are more key. As far as the substrate, I think you you can do a little tweaking and you'll be fine..what I mean is this; the fine gravel underneath can suffice especially over time with the colonization of bacteria and other waste that gets trapped in the lower layer of your tank. What I might suggest is rather than buying a boat load of vermaculite or the such, what i did for example is just place some planting substrate under the area where I planted only. It's a cheaper approach and less disruptive if you have a tank already up and running.
Here's where my expertise (i use this word cautiously

, runs thin....1) I don't know the number or size of fish that can sufficiently respirate enough to provide C02. 2) I don't know, but would guess that benficial bacteria does contribute to C02 levels. I have read that to sucessfully grow most plants, lightly planted or otherwise, one should have 15ppm - 25ppm of C02. Further I've read that you can calculate this by testing water hardness and pH and that there are formulas that would give you a rough indication of what the C02 level is. Of course there are "C02" monitors out there as well.
You bring up a great topic as it makes me want to go back to my LFS which is quite good and further study thier planted tank set up that I buy from....Thier lighting is excellent, excellent substrate and two larger fish, I mean large (don't know the species) and, their plants are great...even so that they pearl..which is you can see the 02 on the leaves...rather amazing. But honestly I have never noticed if they're infusing C02 or not. Next time I'm there, I will look and ask and from what I learn, I'll pass it on.
I suppose in short, if you start out as you've stated, and the plants look healthy and gare rowing then it is working...as they say "if it ain't broke, don't fix it"...one can always make adjustments later. As I enjoy gardening, especially roses and rhododendrons, There are a ba-jillion theories out there...my neighbor does very little in terms of feeding, soil amendment and she has got some roses that are a knock-out....as Mies Van Der Rohe (architect) once said, "Less is more".
Have I wasted your grey matter here with all this? hope not, sounds like you've been well around GF & aquariums long enough to follow the first rule: instinct and intuition! Just the fact that you seeking out information and opinions, I doubt that you'll make a drastic mistake. Finally, if we all knew everything from the go, what fun would it be?...otherwise we would the one's writting books and owning a GF & plant store