While what you say is partially true and some of these problems might be difficult to solve or even impossible to solve during Musk's lifetime, for the most important of them the reasons that might prevent their solving are not technical.
There is no need for a million colonists to achieve self-sufficiency. Even one hundred thousand is much more than enough. The only reason for which a large number of colonists could matter would be to ensure enough genetic diversity for a colony that would lose contact with Earth.
For manufacturing all that is needed, the number of colonists is much less important and the main obstacle is not technical. The most important obstacle is that you cannot go e.g. to a library and learn how to make everything that must be made in a self-sufficient colony, because there is a huge amount of know-how details that is hidden in the trade secrets of thousands of companies scattered around the globe.
None of this secret know-how is something that could not be rediscovered by a good engineer, but rediscovering how to make everything that is made on Earth now is indeed a job for at least one million of engineers.
So for a self-sufficient Mars colony it matters very little how many colonists would be sent there, but it matters if it would be possible for the colonists to license all the technologies that are required for making everything. Most companies existing today might not want to license their technologies at all, or they would request a very large amount of money for that and a Mars colony could not produce anything valuable enough to pay such licenses.
So besides financing the transportation by SpaceX, the creation of a Mars colony would need a many times larger financing for licensing manufacturing technologies, supposing that there would be any willing providers.
Many of the existing manufacturing technologies would need a lot of research to be adapted to Mars conditions, mainly to make them less wasteful and to improve recycling, but in general the Mars ambient conditions, i.e. the lack of an oxidizing and humid atmosphere, can make most manufacturing processes simpler, not more difficult, except for the fact that it may make cooling more difficult, as the Martian atmosphere is useless for that, so the use of other cooling fluids is mandatory.
You seriously underrate the broad expertise by millions of professionals needed to sustain just global electronics manufacturing.
A clear majority of colonists would necessarily be wholly occupied with just keeping the colony alive, breathing, and eating. So an extra population to do electronics, another for chemical engineering, another for mining, another for medicines, more for plumbing and electrical wiring, construction, pilots, drivers, agronomists, programmers, economic planners, dieticians, physical therapists, optometrists, lens grinders, glassmakers ...
There are reasons why exactly zero societies under a million sustain any of these industries domestically.
As a professional electronics engineer with direct experience in semiconductor devices and integrated circuit manufacturing, I can be completely certain that there is absolutely no need for the expertise of "millions" of engineers to do that, but at most for the expertise of a few thousands.
The expertise of "millions" would be needed only when none of them has the practical experience about all the details of how something is made and they have to design all the technological processes from scratch, instead of just improving and adapting a set of known technological processes.
While indeed I am not aware of any society with under 1 million people that was able to sustain all these industries domestically, some decades ago there were a few countries in Western Europe and many of the countries from the Eastern Europe enslaved by the Russian Communists, which could have been entirely self sustained for all the industries, while having a population of only a few millions.
Moreover, the population actually involved in the industries was no more than a few hundred thousands in each country.
Already after 1980, and especially after 1990, the globalization has destroyed the local industries and none of those countries could be self sufficient now.
However the reasons why that has happened have nothing to do with technology or with the human potential of those populations.
Had those countries been kept insulated from external influences, they would have remained self sufficient until now. There is no doubt that technological evolution would have been slower inside a smaller society, but nonetheless they would not look too different from what we have today, e.g. many such countries could manufacture a personal computer with domestic components at that old times, so they certainly would have been able to make better computers 30 years later, even if not so fast and small as we have today in a globalized world.
A smaller society has increased risks of failure, but those risks have nothing to do with technology or with the human potential of its engineers and technicians, but to factors like a parasitic political class which grabs all the power and which also prevents the other people to do properly their jobs, like it happened in the Communist countries.
It is always inspiring to hear scientists disparaging engineers, and engineers downplaying the importance of technicians and of all the support apparatus, materials, and consumables that enable them to do their own work, and all the skilled people needed to develop and produce those reliably on demand.
I thought maybe the experience of supply chain disruptions in the past couple of years would remind people of their dependence, but apparently memories are short.
There is no need for a million colonists to achieve self-sufficiency. Even one hundred thousand is much more than enough. The only reason for which a large number of colonists could matter would be to ensure enough genetic diversity for a colony that would lose contact with Earth.
For manufacturing all that is needed, the number of colonists is much less important and the main obstacle is not technical. The most important obstacle is that you cannot go e.g. to a library and learn how to make everything that must be made in a self-sufficient colony, because there is a huge amount of know-how details that is hidden in the trade secrets of thousands of companies scattered around the globe.
None of this secret know-how is something that could not be rediscovered by a good engineer, but rediscovering how to make everything that is made on Earth now is indeed a job for at least one million of engineers.
So for a self-sufficient Mars colony it matters very little how many colonists would be sent there, but it matters if it would be possible for the colonists to license all the technologies that are required for making everything. Most companies existing today might not want to license their technologies at all, or they would request a very large amount of money for that and a Mars colony could not produce anything valuable enough to pay such licenses.
So besides financing the transportation by SpaceX, the creation of a Mars colony would need a many times larger financing for licensing manufacturing technologies, supposing that there would be any willing providers.
Many of the existing manufacturing technologies would need a lot of research to be adapted to Mars conditions, mainly to make them less wasteful and to improve recycling, but in general the Mars ambient conditions, i.e. the lack of an oxidizing and humid atmosphere, can make most manufacturing processes simpler, not more difficult, except for the fact that it may make cooling more difficult, as the Martian atmosphere is useless for that, so the use of other cooling fluids is mandatory.