The second article, highlighted above, provides the most detail
In summary, 95 HST sets were originally authorised:
Batch 1: 27 sets for the GWML
Batch 2: 32 sets for the ECML
Batch 3: 14 sets for the South West
Batch 4: 18 sets for Crosscountry NE-SW
Batch 5: 4 additional sets for the ECML, having originally been requested as seven sets, but then reduced to just two but later increased following a public outcry.
Initially, there were intended to be 42 East Coast sets, 16 South West sets and an additional eighteen sets for Crosscountry, mirroring the NE-SW build, that would have covered the Glasgow/Manchester to Bournemouth/Brighton axis, but as is now well known these services continued to operate with class 47 + mark 2s right up until "Operation Princess".
Interestingly, in the design stages there were also thirty sets set aside for "other routes" such as Transpennine and Edinburgh-Glasgow.
All but the ECML sets were classified as class 253 and were seven carriages in length: The East Coast trains were classed as 254 as they were originally intended to incorporate higher powered 2500hp engines in order to cope with the additional weight of the eight car formations on the East Coast.
The Midland Mainline fleet was not formed up until the eighties, made up of five sets from the Western Region, three sets from Cross Country and two sets from the ECML, brought about largely by tightening up diagrams.
There are now:
54 sets with FGW
14 sets with East Coast
10 sets with EMT
5 sets with Crosscountry
3 sets with Grand Central
Giving a total of 86 sets.
The biggest change has been the extension in length of most HST sets, even after the construction of the TGS vehicles. The NMT makes use of a good few mark 3 vehicles from the prototype HST, IIRC.
I believe that 43008 is the most travelled power car. I think that it's covered over 8 million miles at this stage, although most of the other power cars probably aren't that far behind. Given that a typical set can cover around 1000 miles on a single pair of tanks of fuel, and many are rostered to cover such a mileage in a single day, this isn't surprising.