Will one who died, owing many prayers due to ignorance of the obligation of ghusl, and was unable to make up all of them before his death, be held accountable? And does merely feeling movement in the private parts invalidate wudu'?

Making up missed prayers is a matter of scholarly disagreement. The questioner must make them up in a way that does not harm her body or livelihood. She can make up two days' worth of prayers each day, following the opinion of the Maliki jurists. If she makes them up in a prescribed manner, without negligence, then she bears no sin even if death overtakes her while she is making them up. Vaginal discharge does not necessitate ablution unless the exit of something is certain.