What type of tank does he want? Fish only (FO)? Fish only with live rock (FOWLR)? Are you certain he doesn't want a reef? It can make a difference when it comes to lighting and filtration choices in particular.
IMHO there are many ways to skin this particular cat - the Fluval 404 should be just fine, though if it's going to be a reef it may not be the best method since these filters can be very efficient at creating nitrates. Wet/dry falls into the same category, they can also become 'nitrate factories'; for reefs, many people use only live rock and pumps for circulation along with a protein skimmer and possibly a sump/refugium.
If you set up the tank with the Fluval buy NEW bio media, don't reuse the old stuff from the FW tank. Also you don't have to stay away from chemical media, carbon is great for keeping the water clear and removing organics and there are other products designed to perform specific functions, such as lowering phosphates.
I also agree that a skimmer is a good idea, no matter what type of tank he sets up.
I don't have years of experience with marines, but I think I can offer my opionion in this case; my 65g FOWLR is doing wonderfully with 65lbs of live rock, 4 powerheads, a skimmer and... a canister filter!
Rule #1 with SW tanks - don't listen exclusively to the LFS, do lots of research. Check out sites like this one and
www.reefcentral.com for loads of information.