Your almost their barny the same problem i had years ago your having now.
Trying to get a set of mechanical rules to make your selections is almost impossible based on the ever changing things that happen in racing.
I collected 10-15 years of sportmans truth formguides herald sun liftouts etc.
Then attempted to induce a selection criteria based on any number of variables days form patterns barriers p/money p/post order etc etc.
These would work for a while then eventually lose so i would go back in time apply new filters to weed out the losers thus creating a new system.
Would then start again with obviously a new system same result lose again
After several years i gave up and joined several rating services while i won for a while eventually the one's i were in lost so back to keeping the day job.
i then joined punters choice who analysed most rating and mechanical data
i joined the most profitable ones unfortunately most only bet saturday's also purchased every profitable mechanical system.
These would grind out a few % profit then eventually die off years later.
Attending the races here in melbourne religously every saturday for years i met a couple of professional punters one particular saturday i summoned up the courage to ask how they made a living out of the punt.
Both said they purchase the ratings from successability or superform eagleform think they published a guide back then called the wizard
then made there own adjustments wait for it based on mechanical rules.
The trick then is to get a set of ratings (1st) zipform r+s( don scott) or the (neurals )these will way up each horses chances against each other using whatever criteria they use you can then apply the statistical side of it to improve the s/rate.
AT least this way you will have the selection criteria being assessed exactly the same way for each race.
Failing that the only other way is to purchase a data base for several $1.000 dollars and go back in time using ratings and mechanical rules.
Unfortunately this is impossible using r+s as their system only keeps the data for a couple of days and is then deleted due to the vast amount of information that is presented on the site.
cheers
garyf.