If you have taken it down farther than you can remember how to reassemble it, it's time to take it to a gunsmith.
If you are determined to do it your self, there are several books on shotgun disassembly/reassembly. Check out DBI publishing or Amazon.com to find one which has your shotgun.
This would be a 12 ga. BPS (Hunter model) pump shotgun made in 1984
50-500 usd
50-500 usd
It came with the Invector system which allowed changing chokes.
A Browning field model bps shotgun is worth between 170-265 dollars for a shotgun with between 60%-90% of its original finish remaining,and a good bore.
Depending on condition $300-$450
Depends on condition and whether it has the original box and papers.
Browning Pump Shotgun "BPS"
1991
Check gunbroker.com for current sale prices and value trends
Seems about 50.00 dollars to high
Impossible to answer without a detalied description of condition.