We already have an electricity grid. Adding charging stations is easy.
Well, yes and no. A Tesla supercharger charges at 125kW and let's say an average car will be on charge for 40 minutes. An ICE car (or a hydrogen car) is charged in - say five minutes, and takes a few hundred Watts each. So to provide the same level of service to Teslas (i.e to charge the same number at the same rate) as a single fuel pump you need eight superchargers. These will take a total of one MegaWatt.
A typical UK motorway filling station will have about 30 pumps, so an equivalent one equipped with 240 Tesla superchargers will take 30 MegaWatts. This is sufficient to power a town of 150,000 UK homes (or about 60,000 US ones) and requires a large substation. Generating capacity would have to be boosted as well as transmission lines to support the increased demand. My (very) rough estimate is that if the whole of the UK switched to BEVs we would have to boost our power network by about 50%
The bottom line is that it is not quite as easy as you seem to imagine.
We do not have any hydrogen infrastructure - hydrogen production is difficult. Hydrogen distribution is extremely difficult. Then we would need to build a LOT of hydrogen filling stations - these cost $2 Million each. They only can fill about 15 cars / day.
There is already a hydrogen infrastructure. There is an industrial demand for it independent of transport needs. It is not particularly difficult to produce it - it needs a lot of energy, but it can be produced very easily in an oil refinery, or by electrolysis. Transporting it by tanker is no more difficult than any other fuel - you just need high-pressure tankers. I imagine that adaptation of an existing filling station to supply hydrogen vehicles costs a tiny fraction of $2,000,000 - possibly $50,000 a pump in a largish roll out. (It is stored above ground, so doesn't involve excavation to house a tank) A pump can fill a vehicle in around 5 minutes, 12 an hour, or 288 a day.
The rest of your post is based on your figures which I believe to be largely incorrect so will not pursue it in any detail. I imagine that what will happen is that filling stations will do what happened in the UK when diesel became popular. Gradually they replaced petrol pumps with diesel ones on a one-by-one basis to meet the growing demand.
I will agree that if hydrogen cars really take off, in your country or mine, it may prove difficult to meet the demand for hydrogen quickly, but I have little doubt that it can be done. A growing number of countries are now finding they have excess energy - GigaWatts of it - at times and this would be quite easily utilised in making hydrogen which can be stockpiled until needed. It is a fuel which fits well into what is becoming an increasingly renewable-based electricity supply industry.
Finally, I would remind you that
domestic electrolysis plant powered from rooftop solar panels are also a distinct possibility. Were these to be mass-produced the cost might well be affordable to many who would normally fill their cars at home. The average motorist does only 40 miles a day, so provided the plant produced a little more than this, the excess could be stockpiled to meet what would be required for a longer journey. This would work better in parts of your country than mine (the UK) where overcast skies are the norm, but the net result of it would be a reduction in the need for filling stations which would be needed only for people making long journeys and wishing to fill up en route.
I enclose a pic of a typical hydrogen storage facility suitable for a filling station. These are capable of 900 bar pressure and could either be charged from a tanker or delivered ready charged from a truck, given suitable unloading equipment which would be quicker.