In your area, would an HRV work better than an ERV?

If you are doing solar, why not consider batteries and get rid of the generator? You could still feed back to the grid.

Make sure you properly size your overhangs to take advantage of passive cooling and heating.

RE: Hot water heater. More efficient to use a condensing model(exhaust thru PVC pipe. If always running out, consider a tankless. Be careful about capacity levels. Quoted output is with a very small temperature rise. Need to look at chart with capacity by temperature rise to size properly (size based on lower of max well output or number of simultaneous users).
If using more than one unit, consider locating in different areas of house to get quicker hot water. Pay attention to minimum flow rates to start/maintain heating (Rheem models very good at this)
If you go this route, consider solar water heater as a preheater with tankless unit to bring up to final temperature.
Alternatively, buy a tanked unit with very high BTU output (e.g. Polaris) and/or set hot water heater to a very high temperature (140+F) and use a water heater extender valve to blend down to operating (nonscalding) temperature after it comes out of the hot water heater. (This is not super efficient, but practical if not going tankless)

Regarding electric: Make sure using production+distribution cost for your utility cost. If 10 cents/KWh is your true total cost, hard to justify solar electric. In most areas, it is around 10 cents for production plus 5 cents or more for distribution

Regarding insulation: If you have 2x4 walls, almost definitely need closed cell foam insulation (a form of spray foam) to achieve any reasonable R value. Pay attention to windows and doors. Energy loss through these is quite high since R values much lower than walls. Insist on high R value/Low U-value
Air filtration: ERVs do minimal filtering and this is not what matters. Forced air HVAC should do any air cleanup. Use a 5" deep filter box on HVAC with a high end pleated air filter or alternatively an electrostatic precipitation type box(has power and electrical to knock out fine airborne debris(e.g. Lennox Pureair). GSHP value depends on the quality of the install. If it is deep enough and the installer does not skimp on the amount of outside coil used these can be very efficient.

My advice is drop the "ROI" requirement. It is essentially useless. Historically, anything with a payback period greater than 9 years has a negative financial impact. Currently, anything with a pay back period greater than 4 years has a negative financial impact, but I wouldn't use the 4 years to make a financial decision, additionally, mortgage money is essentially free right now. The unfortunate problem with any "efficiency" is that rarely do they make financial sense. Even spray foam insulation has a bad ROI.

I am not saying, don't do these things. I am saying take a different look at these things. Do away with the whole "ROI" requirement and just look at the price for items that are going to make you more comfortable. If the price seems too high for the enjoyment and benefit you are going to get from it then scrap it.

Now some finance stuff that is probably too much like being back in school and way above what you asked so you might want to just stop here.

ROI = (gain from an investment - cost of investment)/cost of investment. This will always return a percentage. The percentage is then compared against other investments. What you have been talking about is not an ROI but a payback period. Which is not a big deal but understand that companies don't use payback period to make financial decisions because it doesn't consider the time value of money. Put simply a dollar today is worth more than a dollar in 10 years. The reasoning is that you could put the dollar in the bank and grow it. The tool most often used by sophisticated companies to make investment decisions is Net Present Value. You can jump on Youtube and look it up if you want but an easier way to think about it is just to use a Present Value of an Annuity Calculator, the one here at Investopedia is easy to use. In the top box (interest per time period) enter 5 if you are very conservative and 9.84 if you are fairly aggressive, or anything in between (5% is historical T-bond and is essentially risk free and 9.84% is Stock market since the crash.) In the second box enter the amount of time you plan on having these savings, and in the third enter the amount you expect to save annually. If that amount is more than you are paying today it is a good investment. If it is less then it is not a good investment. This is still a rough calculation to get a good calculation you will have to use a Net Present Value calculator.

Sorry it is so long, I hope it helps.

Regarding spray foam: It is cheaper to build 2x6 walls and use fiberglass, but fiberglass in a 2x4 wall will not meet minimum code requirements and result in a drafty house. Either spray foam or a styrofoam type board on the outside (in addition to fiberglass in the wall) would be required by most area building codes just to get to code minimums. Payback on this should be reasonable. In addition, a well insulated house is less likely to feel drafty as constant air temperature is easier to maintain in a room that does not have a high rate of heat gain/loss at the outer wall. Use of a heat pump makes a house feel more drafty than a conventional HVAC system since a heat pump is set to output air at near room temperature and move it around as needed for even distribution.

ROI/NPV etc: If you are taking out a mortgage, the mortgage rate would be a good discount rate to use. If you have surplus savings, the current risk free rate is around zero after adjusting for inflation. Longer term investments appear to yield more but are likely to lose value if interest rates start rising as most experts expect. Energy efficient doors and windows are almost always worth it, front loading washing machines and gas/propane(not electric) dryers and hot water heaters generally make sense. Minimum code insulation to walls and ceilings makes sense in the long run. None of us know future energy costs for certain, but energy efficiency reduces our vulnerability to any future price spikes. Of course, if energy prices stay low, they are a poor investment in hindsight, but so is property and life insurance most of the time (if we live and the house does not burn down)

While I agree with much of what you said zver I have a few concerns (1) the mortgage rate should never be used as the discount rate, in fact it should be added to the discount rate as those are charges you must overcome for financial benefit. (2) Investments are reinvested at the current rate while mortgages are fixed. A rate increase will cause NPV to look worse while simultaneously making comfort investments look smarter. (3) The energy rate increase is something to consider but even running worse case scenarios don't often return favorable NPV. (4) The risk free rate is not zero when inflation adjusted it is about 2% which it always is add the 4% mortgage hurdle and you get 6% take off 1% for tax advantages and disadvantages and you get the 5%.

All said none of this really matters. My advice is not designed to encourage you not to do these things, but to drop a false hurdle to their acceptance. Something that makes you happy with a 20 year payback may be better than something with 15 year payback. They are both probably bad investments but screw investing if you are happier.

Research Passivhaus. Will add 10% to 15% to the cost of a new build. Will reduce energy use to 80% below basic energy star home. Will almost eliminate HVAC costs. Will not need the expensive geothermal. Will have a house that has great air quality (many ways to get to the super airsealed and insulated Passivhaus standard so no need for the VOCs of spray foam) and is quiet. You can add a bit of PV for electric later. You can put electric heat (IF you need any heat at all) and get that through Few PV panels.

altf - are there any Passivhaus designers in the US? I was unable to locate any. Thanks!

You might also search "Net Zero". But an energy efficient house is not the same as nontoxic allergy-safe house, so be sure to ask for both.