Nomenclature priorities with ethers, acyl groups and ketones
In principle, your assumptions about the order of priority for classes is correct. According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), the order of seniority of classes in decreasing order of seniority is as follows.


  (…)
  7. acids
  (…)
  9. esters
  (…)
  15. aldehydes
  16. ketones
  (…)
  42. ethers
  (…)


Thus, it is correct that the names for all compounds given in the question have the suffix ‘oic acid’.

However, the names proposed by you still contain a few errors.

Your name “(2-oxopropionyl)oxy butanoic acid” is ambiguous since the locant for the complex substituent group ‘(2-oxopropionyl)oxy’ is missing.
The complete name is “4-[(2-oxopropionyl)oxy]butanoic acid”.
However, the preferred name is 4-[(2-oxopropanoyl)oxy]butanoic acid.

Your other names include the correct suffixes and locants; however, the suffixes are not cited in alphabetical order. The correct names are


4-methoxy-3,4-dioxobutanoic acid (not “3,4-dioxo 4-methoxy butanoic acid”)
6-oxo-3-(2-oxopropyl)heptanoic acid (not “3-(2-oxopropyl),6-oxo heptanoic acid”)
6-oxo-3-propanoylheptanoic acid (not “3-propionyl,6-oxo heptanoic acid”)
6-oxo-3-(3-oxopropyl)heptanoic acid (not “3-(3-oxobutyl),6-oxo hexanoic acid”)