Why would the british care if there were french troops in america

Because the British hated the French and feared that the French would try and take over the British Colony

 Because the British hated the French and feared that the French would try take over the British city

Yes, some people used the depression to the max. not everybody had stocks, and those that didn't bought many things inexpensive, so that when prices rose again, they were much more richer than beforehope this