Your Mountain Stalker .50 Rifle was made in Spain for Connecticut Valley Arms. These are lightweight, synthetic stocked traditional muzzle loaders. They sold at dept stores for about $115.
100-400 USD
50-100 USD or so
1200
10-100 usd
$100
You will need a professional appraisal
50-100 USD
50-150
10-100 usd
50-500 USD depending on specifics
41 or 42 ? about 350 $
50-170 usd