For strictly college, if sharing BB and hockey, would be in the ~13-14K range with a seating bowl configuration that'd allow for ~7-8K in the bottom level and the top curtained off for hockey. Thing is, that would only work on campus. Building that in Hartford would make no sense, it'd be too small for major pro sports and major concerts, too big for minor league sports. There's also really no reason to build that in Storrs since Gampel is more than sufficient as it stands.
If the state continues to threaten to screw UConn over, I'd love to see them completely pull out of playing any games in Hartford. The arena and surrounding businesses would crumble without those home events there, while the programs would likely thrive with a completely on-campus environment. Though the hockey team would need a facility built.