Yes, you have six devices using IRQ 11, but that's not necessarily a problem; IRQs can be shared on the PCI bus (but can't be shared across both ISA and PCI busses). Even so, IRQ sharing should be avoided if possible.
To see all interrupts and ioports:
$ cat /proc/interrupts
$ cat /proc/ioports
although sometimes things won't show up in /proc/interrupts if that piece of hardware hasn't issued an interrupt.
Here's an example of setserial:
#setserial /dev/ttyS0 port 0x02e8 irq 3 baud_base 115200
If you ever forget, run setserial with the -G option on any serial port to get an example of how to use it:
# setserial -G /dev/ttyS0
/dev/ttyS0 uart 16550A port 0x03f8 irq 4 baud_base 115200 spd_normal skip_test
is really good. The Serial-HOWTO is where I learned everything I know about serial ports.
Hope this helps,