Thanks for the vid Mark hes got a pretty slick process there. I mostly build my yeast starters off some saved yeast from previous starter.
Sometimes I pitch onto previous yeast cake if I find the beer has no flaws this is a no no amongst brewing circles Overpitching and all but I cant tell the difference.
Sanitation is key to good clean health yeast culturing. Since I've started HBing I've always just bought a yeast strain and pitched consecutively maybe 5-6 gens in then buy a new strain.
Things I look out for to tell me yeast are deviating from mother culture are lower attenuation and lower floculation (if that is an attribute of the yeast of course). And also tasting the starter supernatant before using yeast to guage if there are any funky bas#$ds in there.