You explained it very well. I am in total understanding now.
I don't want to spring for the PAR meter right now, so I guess I will just have to see how my plants do with the current system.
A few other notes… It's better to start your tank with a lot of plants rather than just a few. But you'll have to make sure that you are supplying "consistent" nutrients. You might want to do a search on the "Estimative Index" method of dosing. It's very cost effective to mix your own ferts and add them on a weekly schedule. Two of the nutrients that you need to dose are Nitrate and Phosphate and you can use cheap test kits to validate if you're in the ball park when dosing these.
Floating hornwort is a nutrient sponge. Especially since it receives maximum lighting while floating at the surface. In Diana Walstad's classic book, "The Ecology of the Planted Aquarium" she recommends using floating Hornwort in the beginning stages of a new aquarium setup. Not only will it take the edge of the ammonia/nitrite/nitrate spike you get during the cycling of a new tank, but it also grows fast and you can use it as a metric for your lighting.
You may eventually move away from Hornwort, depending on your aquascaping goals. The only time it looks attractive to me is when fish are actively using it for cover shelter. Other than that, IMO, it's a nuisance and will take over the whole surface if not kept in check.
I have a regular static Aquaclear powerhead. I mounted it on the side of the tank/middle. I will keep an eye on the dead spots in the tank.
Keep in mind, the flow is about refreshing the water over the surface of the plant's leaves. My understanding is that during photosynthesis, a thin zone is created around the leaf and in static waters this zone will hinder efficient uptake of CO2, not to mention depleting the "local" supply of available CO2. By keeping the water actively circulating over the surface of the leaf, you minimize this effect. If your HOB filters are actively perturbing the surface of the water, this will also ensure maximum ambient levels of CO2 (and O2) in the water column.