I'd be pretty crazy about that Dogs unit if they existed. They're pretty ridiculously undercosted though as you propose them. I'd think making them more like Chaos Warhounds at 6 points a model, M7, Ld5, and not fast cav; this would be more appropriate as that's an incredibly cheap awesome unit anyway. I don't think these are very likely to find their way into an Empire book, but I would love it if they did. They would make an excellent throwaway diverter unit.
Regarding the fast cav, I'd use DoW Light Cav for a benchmark unit at 11 points a model for basic human stats on a basic horse. +1 point for spears, shield, or light armor with light armor and shield making the unit no longer fast cav. I do think these would have a place in a new Empire armybook, with the only change required being regular command costs (probably 7/14/14). I currently use two units of the DoW Light Cav as my rare choices in my standard Empire list and find them incredibly handy for keeping frenzied units busy, diverting charges, taking out warmachines, and occasionally getting a flank or rear charge against a soft-hitting target.