boylee,
I would think hard about using filters. They filter out plenty of losers, but also(in my experience) can filter out some decent priced winners, the very horses that can make a system profitable.
When you review your results, spare a little time to see what happened to those horses that were filtered out.
It’s each to their own, I know, but I feel it’s better to have a list of possibles and then weigh up the negatives and positives before comparing chances to available odds.
Trying to eliminate what cannot win(the Sherlock Holmes approach) has its merits, no doubt, but far too often we dismiss horses with only very limited reasoning.