I'm not sure "dual-lan" means what you think it does. Are you talking about putting each of the NICs on the NAS into a separate subnet? Do you have more than one subnet in your LAN? Also, are your switches managed, or just plug and play type switches?
Basically, if everything is on the same subnet, then you'll either only be able to use one of the NAS NICs, or you'll need a managed switch that supports etherchannel/NIC teaming (configuring both NICs to work together as a single, 2-Gig port rather than 2 x 1Gig ports). You won't be able to get that to work over two separate switches.
Putting everything into one big switch is always going to be quicker than daisy-chained switches. That way everything goes over the switch's back-plane rather than wandering around on ethernet links between the switches.
Edit: Cisco do some good layer 3 managed switches for small businesses. Buggered if I can remember their model numbers, though.
Edit edit: what Ken said.
EDITED: 28 Oct 2014 18:45 by PATCH