Flight training insurance: +$4-6K per annum (excluding ab-initio). Be prepared for the inevitable prop strike+engine bulk strip (covered by insurance, but not at replacement cost, at a depreciated level so it'll still cost you lots), loss of hire time (hey nobody compensates you for that, bad luck on your "investment") and countless hours of frigging around with LAMEs, engine rebuilders (if any are left on your airstrip) etc. Also be prepared for early adopter costs relating (e.g. ADSB, could be done with $500 of hardware, but it'll cost you thousands because of early adopter costs) etc. Be prepared to pay several hundred dollars just to contemplate installing a clock or an outside air temperature gauge because you need an engineering order to draw up diagrams and other silly stuff.
Above all, remember, the three F rule.
If it floats, flies or f__ks, rent it by the hour.
Second rule, if you want to become a millionaire through aviation, start with a few billion dollars, then start an airline.