Assuming the other side of Gi 0/1 is also a GigabitEthernet, the most likely cause is a bad cable. You need a cable with all four pairs connected. 100M will work with only two pairs. That is probably why you negotiate to 100M.
For more info on how GE uses all four pairs, see: http://goo.gl/DMYkSM
If you're just using 1 10Gb port to connect them, you only have to add that link into the VLANs you want to share between the switches, if any. Out of the box, there'd be no configuration on your side w/ 1 link
With 2 links, you will want to form a link aggregation in one of 2 ways. Say you're going to link over 1/49 and 2/49 (first 10Gb on both switches in the stack) to ports 1/50 and 2/50 on the 2nd stack (second 10Gb on both switches in the stack). It's like this:
Stack 1:
trunk 1/49,2/49 trk1 lacp
Stack 2:
trunk 1/50,2/50 trk1 lacp
The name 'trk1' becomes the virtual port name. It doesn't have to match on both sides.
The last keyword lacp can also be trunk. The difference is that lacp is a more stateful connection, trunk being static port bundle.
Finally, if you have VLANs that need to transit the trunk, you have to allow those across. Just like the other ports are set up, but with the 'trk1' port. If you had, say VLANs 10 and 20, you'd do this on both stacks:
vlan 10
tagged trk1
vlan 20
tagged trk1
Best Answer
An LACP PDU is around 110 bytes, so running them every second isn't likely to even register on an Ethernet link of any speed.
I would recommend running in "fast" mode at all times for rapid detection of faults.