The Browning wwebsite, under customer service, has serial number ranges for different firearms. Yu should find yours there. VERY nice rifles, great caliber.
That Serail number dates the BAR to 1986.
A gunsmith can help you.
700-1000
You did not provide the sn, so the question can't be answered.
Best to ask a gunsmith for help.
Check the receiver carefully.
Contact Browning Customer Service, and request an owner's manual for your rifle. You WILL need the pictures in it.
What do you want to know?
500 USD
100-1000+ depending on specifics
50-500 USD or more
Best to ask a gunsmith for assistance.