It's not the router which needs to support LACP, it the switch.
Your network interface cards need to connect at the same speed or you won't be able to channel all of them. This shouldn't be a problem since most NICs today run at 10/100/1000 and will autodetect the connection speed. All your NICs from a single server need to connect to the same switch.
Understand that bonding the interfaces will not increase throughput for a single traffic flow. A traffic flow will only use one interface. The increased throughput comes when you have multiple traffic flows since each interface will handle a subset of all the flows.
Channel bonding really works best if you have a power of two (2, 4, 8) interfaces in the channel. Other numbers of interfaces mess with the algorithm used to select which interface will get which flow, resulting in sub-optimal flow balancing.