Short answers, pulled from the story.
Archduke Charles commanded the Austrian host at the Battle of Abensberg. He failed to issue orders from 11:00 AM until 6:30 PM while his forces were split by Napoleon.
Over 3,000 Austrians became prisoners including Thierry after their cavalry was routed near Rohr. Four cannon were lost when French chasseurs and cuirassiers cut down fugitives.
Archduke Charles led a central mass of 209,600 men across the Isar at Landshut on the 16th of April. This force moved slowly but effectively from the frontier to the river over six days.
Emperor Napoleon arrived at the front from Paris on the 17th of April to wrest control back from the archduke. He consolidated his forces immediately upon arrival to counter the Austrian advance.
Hiller resolved to retreat because the extent of Thierry and Schustekh's disaster became known. This decision meant the Austrian left wing would operate independently from Archduke Charles' main body until May 15th north of Vienna.