With the caveat that I started at UB (and started closely following) the year after McCrea graduated, I think the #1 scorer and #3 rebounder in program history needs to be on the wall.
CJ being (imo) the best player in program history also gets him on the wall.
Perkins being another 4 year stud and the #2 option in the greatest era of UB history, and playing in the most games in UB history gets him on the wall.
Jeenathan's case is a little fuzzy to me, his UB career alone frankly probably doesn't deserve to be on the wall, based on how few players have been honored, but him making to the NBA is certainly an important feather in the program's cap and worthy of honoring in my opinion.
I loved Segu in his time at UB, but in my opinion his career is not particularly close to being worth "honoring" his number. He had one MAC second team honor in his career, and never led a MAC championship team, we'd need a huge wall if that is the bar.