How many have been retired so far and when will they be completely retired?
They will be retired when WMATA awards a contract to replace them.
According to wikipedia 76 were procured 1983–1984, Midlife rehabilitation 2002–2004 2 have been removed service, as I recall, because of damage cause by hard coupling in Falls Church Yard in the early 2000s, though that number is likely now 4.
Crash worthiness improvements were made to the 2 and 3k cars during midlife rehabilitation. The 2, 3 and 4k cars were structurally similar to the 1k cars when new but somewhat more rigid.