Do the EPM test first. Better shoeing may just mask EPM symptoms (like tripping) which REALLY need to be treated ASAP if you horse shows a high titer. If the titer comes up within the range of “infected”, have the neuro test done by a good vet who knows what to look for AND how to treat it.
Don’t bother with the spinal tap - just do the blood test and go from there.
EPM isn’t a death knell if treated quickly. That’s why I strongly suggest you do the test first before anything else.
BTW - when he stands, does he stand cowhocked behind? (toes out, hocks in)