Honestly Jeff, if the nutrients are non-limiting then there's not much to play with. If they aren't non-limiting, algae competes in the column and you have to work harder. Tweaking the nutrients is kind of pointless if you're not trying to do fancy stuff like playing with growth morphology.
That 55 gal is about where I'd want to strap CO2 on; perhaps raise the fixture or obscure the light a little. An all-in-one won't do the job with that kind of light. The 7 gal isn't a big deal if some algae happens; it's a small tank. The 25 gal won't need extra PO4 if you're feeding heavily.
If you want an all-in-one, you could try a mix of CSM+B with KNO3. I'd keep some KH2PO4 on hand though; GSA is a pain, and stunted phosphate deficient plants are ugly. At worst EI is a two bottle system with GH booster at water change time if you've got soft water. Rather than keeping it sitting in the fridge, you can simply use HCl (10ml of 14.5% pool acid sold at Home Depot per liter) or I believe 4x the quantity of Flourish Excel. You'll have to mix less often this way and have fewer worries about drinking fertilizer.
In all cases, you're using inert substrate. You are very dependent on what you dose in the tank, completely dependent if you used Flourish tabs which contain just about zero nutrients. For less maintenance long-term, nutrient loaded substrates are a great direction. If you ever end up overhauling, look at the benefits of things like osmocote, mineralized soil/worm castings, ADA aquasoil, etc. Some are dirt cheap, some cost, each have their advantages and drawbacks.
Believe it or not, compressed CO2 is pretty headache free if you didn't need it before; adding any now will just make for healthier plants. The infamous tinkering happens when you strap high light to the tank and compensate for the lack of natural CO2 by using compressed. Without the CO2, it turns into a full scale disaster. It's taken the hobby a while to add this up, but now it's heading towards low light tanks with compressed CO2 because they're both beautiful and easy. If the plants are growing too fast because you added CO2, then they were CO2-limited; simply reduce the light level to slow them. The only real drawback comes with cheap regulators dumping CO2 into the tank all at once (get a decent reg) and anyone who doesn't educate themselves on how to properly handle their regulator (5 minutes talking to LeftC will fix this). It's definitely an investment, but it's also nice to have.
Anyhow, my recommendation would be 9.2g of CSM+B and 65g of KNO3, add what ever stabilizer ahead of time in 750ml DI H2O and wait 5 minutes, add the CSM+B, stir until dissolved, add the KNO3, repeat, top up to 1L. Leave the bottle sit with the cap off for an hour or two (the mix will probably be cold) and away you go. Typically for high tech/light it would be 1ml for every 6L, 3x a week with a 50% WC. It works well for me and my math, but it's easy to convert. Just dose an average of 1ml for every 8L of column over the course of a week. Do this for a month, then do a 50% WC. If all seems clear, you can try dosing/changing a little less often. For the sake of the fish, I tend to change 50% a month as a very minimum anyhow, so I use this method often enough for my own low tech tanks. As I said, keep the KH2PO4 around; if PO4 dosing becomes an issue, you can always mix up a solution of it to dose now and then. If it turns out you need magnesium, about 101g of epsom salts in the above solution added after the stabilizer and stirred then leave to set for a few minutes before adding the CSM+B will solve your problem.
