The Bills were something like 14-2 against the NFC during the Super Bowl run and I think both losses were meaningless games at the end of the season. I think they would've easily made the playoffs in the NFC.
Full free agency started in 1993. Barry played until 1998. So yes they had free agency back then. He also signed a huge contract extension in 1997 to stay there.
I always thought Smith was underrated. He had the worst hands so his interceptions stats were always awful, but I think as far as pure coverage goes, he's as good as anyone we've had over the past 25 years.