How many of Dr Gero's Androids were actually Androids and how many were Cyborgs?
I only listed the ones which are in the canon or in the movies. I haven't listed the ones in the games.

Android #1-#7: Considered failures and destroyed. We don't know much about about them.

Android #8: According to some guides, it (he?) is a cyborg. But let's consider him a fully artificial android because it's not stated in the canon anywhere (I guess).

Android #9-#12: Same as 1-7, destroyed.

Android #13-#15: Non-canon android appearing in "Super Android 13!". May be fully android considering their construction was started before 16, 17 and 18.

Android #16: Pure android.

Android #17-#18: Everybody knows them. They are cyborgs.

Android #19: Pure robot.

Android #20: Dr. Gero himself. He is a cyborg as you said.

So to answer your question, out of 20 androids made by Dr. Gero, only 3 are cyborgs and the rest are fully android.

I've used the android term as a replacement for robot. But android literally means cyborg.

I guess this answers your question.