You will want to connect them using a LAG port configured as a VLAN trunk port. Never heard of a level 2 or 3 LAG if your referring to layer 2 or layer 3 then a LAG is technically only layer 2.  Depending on the hardware you might be able to assign an IP to a LAG making it  layer 3 port but you would only do that if you were using it as a router interface. You just want a normal port-channel between the two switches to carry your VLAN traffic.  Pretty easy to do.1.  Create a LAG.2.  Add interfaces to LAG.3.  Configure LAG as a trunk port.4.  Add allowed VLANs to LAG trunk.5.  Connect switch1 lag interfaces to switch2 lag interfaces. If you need specific commands for doing it Ill have to find the manual for those switches.  I have never used that particular model of PowerConnect.  After you get that done you should probably do some testing to make sure it works like you want. Current I only have 4 GigE interfaces in the LAG between my 6248s but if I start running an iSCSI SAN I would probably add another 4 or use 10GigE interfaces.  Given you have a total of 6 GigE interfaces on your SAN I would probably use at least 4 GigE interfaces in the LAG if you can.
Currently I have Equallogic PS5000, two PowerConnect 5424 switches, two Poweredge 2950 and one r610 servers running RHEL 5.  At a moment I have connected two interfaces of one controller in one switch and one in another. The switches are not interconnected.  I am using multipath in servers having two Broadcomm 1GB ports for ISCSI in them one going in each switch.  Is this the recommended solution or can anyone give other recommendations?   Thank you for your help, Arto
ISCSI network configuarion guidelines