Well water of city water?

Are you certain you start with an acid neutralizer now? Why? If your pH is over 7, it's not necessary. Are you able to take a sample immediately after your pressure tank, before any treatment equipment and retest? What type of acid neutralizer is being used?

What do you mean by "immediate onsite acid test?" pH? If a pH is what you meant, was the meter calibrated immediately prior to use?

Your plan:

If you do actually have low pH water, your proposed treatment plan does not address that issue and your water will eat your pipes, not to mention your teeth. Even if you only have periods of low pH, you are going to have to address this problem.

Filox is a very dense material. You do not have adequate flow to backwash it.

Nobody can tell if a $2000 or a $20,000 aeration tank is good quality without knowing something about its components.

If water taste is your only concern regarding minerals, you can run a line to your sink after iron removal but before softening for drinking water. At your current hardness levels, you will have problems with hardness scale. If acid neutralizing is necessary, your hardness will be raised to a very high level and cause damage to water heaters, faucets, pipes, etc.

If you have a pH meter, know how to calibrate it, and have a location to take samples upstream from your treatment, sample and track pH for a week or so and see what you have. Measure the pH immediately after taking the sample to maintain accuracy.

PH: At home purchase, PH test failed due to low PH after all treatment equipment requiring seller correction. Selelr responded that minor adjustment needed. First tank is backwashable and has consumeable. Quite sure it is acid neutralizer. Surprised by recent test results. Most likely carbon dioxide is source of acidity, so aerator should help maintain reasonable PH. Most of supply plumbing was replaced by prior owner (copper to CPVC) implying there had been a problem. He had tried to use ResUp for iron. Not sure if this contributes to PH issue. Immediate onsite test was calibrated PH meter with sample bypassing all treatment and water run long enough to flush out treated water.

Filox: Planning on 9" tank(1 cu ft) with Vortech unit which requires 6.6GPM cold water backflush which is within allowed parameters. Peak supply water flow a little high for unit, but rare and result of high flow is slightly reduced iron removal for a unit that is way more powerful an iron remover which is operating with plenty of dissolved oxygen in water so should not be an issue.

Aeration tank: Thinking of waterefining.com's AER01I. Looks like reasonable components, though I welcome any feedback on this issue. With a 1/2 HP motor and 200 Gallon tank it sounds capable of providing adequate flow for backwash of filox filter. I have contacted the vendor about flowrate, but not received any response.

Hardness: This is tough. Feedback is that water is too hard before neutralizer for not softening (One of reasons for aerator is to avoid acid neutralizer and resulting increase in hardness). Separate water lines to kitchen sinks impractical due to house layout(finished basement ceilings, very long runs, 2 inlaw suites and bar sink as well as main kitchen...)
Am trying to research salt-free water conditioners (TAC). Know magnet/electric units worthless. TAC units cite Arizona State study that they work. Pass water through catalyst medium. Claim to form stable crystal structure that keeps calcium from depositing.

Most likely carbon dioxide is source of acidity

Without testing - that is a guess. Testing is not difficult. Make certain before you design your whole treatment program around it. If you have high concentrations of CO2, aeration will work well. However, if you have low concentrations of CO2, aeration doesn't work well and the addition of an alkali may be required instead of or in addition to aeration.

You mentioned hydrogen sulfide removal. If it is, in fact, a problem, aeration only removes it if pH is below 6.

Filox: If you only backflush it with 6.6 GPM of cold water, you will run into a problem. The stuff has a high density - it is not physically possible to obtain an adequate backwash with that low flow rate. If you look at the manufacturer's physical properties sheets you will see that recommended backwash for 1 cuft is 12-15 GPM, not 6.6 GPM. At 6.6 GPM you are only going to get about 3-4% bed expansion - a recipe for rapid bed failure.

Aeration tank: An aeration tank is not a terribly complicated device. My only caution for the tank you have chosen is the "proprietary unique" aeration nozzles. Translation - much more expensive to repair/replace when it becomes necessary (and it will at some point become necessary).

Hardness: I've not been impressed with the TAC systems I've seen - their "scientific" explanations are dubious at best. Although passing supersaturated water over a pre-formed crystalline structure will encourage formation of crystals, it will not and cannot cause all or even most of the calcium in the water for for a stable crystal structure. Once the water is no longer supersaturated - no more crystals for and you are still left with hardness in your water, plenty to continue to build up scale in your hot water system. The ASU study showed some promise. However, it was a very cursory study with some questionable methods, not repeated and not long term.

First, thanks for your responses.

RE: Carbon dioxide as source of PH. Admittedly speculation. Common source around here. PH moves toward neutral on exposure to air furthers suspicion. Not sure how to test source of PH. Would welcome any suggestions. I agree that undesirable to buy expensive equipment without being sure.

RE: Hydrogen Sulfide. Assuming Filox will catch most of it. Aerator provides oxidizing agent.

Filox: Have 7.5+ avg gpm available for backflush(averaged over pressure tank fill. 6.6gpg is manufacturer's spec for tank. Note that product specification for Manganese Oxide products is based on surface area not volume. So tall stack easier to backflush than wide one. That being said, I have no real world experience and am just going off manufacturer's specs which may be optimistic. Also nervous about lack of response from Aerator provider on GPM output as this will be the true source of backflush and not the well (200 gallon tank and its own water pump and pressure tank)

RE TAC systems. I wish some approach like this would work, but as I search for information not biased by people trying to sell products, the AZ study is the only one I saw and, as you said, it is not real world conditions. I have two 20 year old hot water heaters. I will keep my old water conditioner in basement and might "experiment" by leaving hardness untreated and see how bad it is when they fail or are replaced in a few years.