Short answers, pulled from the story.
The British government aimed to seal the Scheldt estuary and destroy the French fleet thought to be hiding in Flushing. This mission also intended to provide a diversion for Austria during their struggle against France.
A massive force of 39,000 troops crossed the North Sea from The Downs with 37 ships under Sir Richard Strachan's command. This represented the largest British expedition of that year.
Over 8,000 men fell ill due to what became known as Walcheren fever which likely combined malaria, typhus, typhoid, and dysentery into one deadly mix. Medical provisions proved inadequate despite reports that an occupying French force had lost 80% of its numbers years earlier due to similar sickness.
Napoleon approved the appointment of Marshal Jean-Baptiste Bernadotte who arrived to defend the Netherlands after resigning his command following displeasure at the Battle of Wagram. He brought genius for organization and training to the chaotic defense while heavily reinforcing Antwerp.
The British government spent almost £8 million on this failed campaign while more than 4,000 British troops died during the expedition. Only 106 were killed in action yet many others remained permanently weakened or caused a permanent doubling of sick lists in the Peninsular War.