Simon, The 2 main issues you mention are Lack of gravity and radiation. These have been considered by spacex and have been deemed acceptable risks. First radiation exposure for the trip is estimated at 1% increase in health risks, so if you get a smoker and take him to mars and not give him cigarettes, you get a net reduction in health risks for that person .
The BFR is an interplanetary ship with “gravity” if you join 2 of them together (which they already can do) and spin them. However, they may not want to do that due to Operational Risks and accept the loss in bone density and muscle degeneration as acceptable risks which was shown to be quickly recoverable(on earth) once they land on mars with 38% gravity… Note we dont know what 38% gravity will do for the human body in terms of recovery. but They have deemed it as acceptable risks and expect good recovery. I would think spinning up 2 crewed Mated-BFR is a good option. Problem is the solar cells will only be half as efficient. Maybe they need to mount the solar cells on a central mating non spinning section… but its probably too complex to do in time. Or just use nuclear generators …
the 1% increase in health risks due to transit radiation has been deemed acceptable. the radiation on the surface of mars can be mitigated someway by good dwellings materials. There has been research results learnt from the ISS as to what material helps. and i am sure it will be applied on mars … Excavating underground dwellings has been considered and will also probably be built over time.
The plan has been that there will be a total of 6 BFR on Mars, that is landed mass of 150*6 = 900 metric tonnes (including humans). That seems to be enough supplies for 3 years and tools.
Dont be overwhelmed by “everything” and do nothing.
There are lots of other issues you have not mentioned… and they have been considered and mitigated or the risks have been accepted. My biggest concern is the perchlorates (Poisons) in the soil and dust. … Cant see how they can mitigate that effectively without the whole team dying within the 3 years mission or after they comeback to earth .