Portnumbers in the range 49152 through 65535 http://www.iana.org/assignments/port-numbers

As for simultanious downloads, it all depends on your downspeed and system. I don't use Limewire anymore, so nothing works best for me.

Uploads should be throttled at at least 5KB/s under maximum and if acting as an UltraPeer probably closer to 15KB/s under maximum.