200 amp feeder wire size?
Your 350/350/4/4 AL for the 400A entrance cable from the meter seems undersized.  even using the residential NEC 310.15 83% of 400 for 332A would require 500KCMIl for the hots and 300 KCMIL for the neutral using the 70% rule at 90C (if your utility allows that).
Unless I missed your point and you are protecting this line with a 200A breaker from the 400Amp panel to feed the future house. (and then, your wire seems perfect!)