Should I sear meat which is cooked sous vide before it goes in the bag, or after

You could use oil, but I don't think it's worth it; realize that you're going to be using additional energy for obtaining, cleaning, and disposal of it.

Regarding using a broth with a porous bag, well, that isn't sous vide. That's more akin to a slow-cooker. The whole point of sous vide is the airtight barrier between food and heat.

Update

Oil does not have a higher thermal mass than water. Ammonia does, but I'd suggest avoiding that. ;)

Source: http://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html

The beer cooler hack is not ideal for meat. The issue is the cooking time. I don't find Sous Vide to be particularly good for meats with low fat content that require short cooking time. The meat comes out perfectly cooked, which is nice (i.e. a steak medium rare from edge to edge), but you don't get any real wow factor from the flavor or texture. Where meats start to get really interesting, in my opinion, is long cook times. Tougher cuts of meat that require longer cooking (short ribs, flank steak, ribs, roasts) come out meltingly tender with all the lovely meaty flavor of the cut and you can cook them medium rare. These take 12-24 hours though, and I don't think the beer cooler hack would work for that (at least not without a lot of tending).

However, the beer cooler hack should work very well for seafood, which has much shorter cooking times. Here the temperature control and the vacuum sealing is what really makes a difference. You can get some wonderfully novel textures out of seafood and very subtle complex tastes without anything being "fishy". I'd recommend you try one of the following:

• Salmon Mi-Cuit - cook salmon at 113F / 45C for about 35 minutes. This is delicious. Somewhere between sashimi and cooked, great texture and a fantastic flavor.
• Lobster - cook the tail meat (no shell) at 140F / 60C for 15 - 20 minutes. Do not let this one go long. The lobster will turn to mush and gets disgusting.
• Halibut - cook at 140F / 60C for about 35 minutes. Great texture and flavor. Very moist. Essentially "perfectly cooked" fish.

Note that the first two do not reach pasteurization levels. You should use sushi grade fish and not serve to anyone who is immune compromised.

You could also try chicken breasts. I know a couple of people who rave about chicken because of how moist it comes out, but I've never had much luck with it (the few times I've tried).