Ah, that makes a bit more sense if you're sharing that filter between 5 people.
>Also, how do you setup your tarp in less desireable weather?
First off, I should clarify that I mostly use the Trailstar, which offers much more protection than many tarps.
If it's raining or snowing, I lay the tarp out and put my pack under it. I begin staking it quickly, knowing that I can/will adjust the stakes once the tarp is up. I try to pitch it according to conditions (the door facing away from the wind, and as low to the ground as needed). As the shelter takes shape, I just restake if needed.
If it's windy as well, that gets a bit more difficult. Again, just pegging the corners down to control it helps a lot. You can always pull up a peg and restake as necessary. This is where practice and knowledge comes in. I am by no means an expert, but can get the job done.
If you have to set up in deep snow, you need to know how to use deadman anchors and how to work-harden the snow. Since a tarp requires tension on the guy lines to hold it up, this takes a bit more patience than staking down a tent whose shape is formed by poles. For example, on my last trip I had to let my anchors sit 15 minutes before even thinking about erecting the center pole.
If there is no/little snow, but the ground is still frozen, make sure you have very robust stakes like MSR Groundhogs. You can pound these into the frozen ground with a rock. Bring an extra just in case you snap one (rare).
>What other cautions do you take besides just the tarp setup (pads, fire trenches, etc)
Site selection becomes pretty important. Look for natural windbreaks. As with any shelter, always look above you to make sure there are no dead/weak branches that could fall on you. Sleeping under tree cover can also help reduce radiation cooling. Valleys and depressions is where cold air settles. Consider this for site selection.
Under a tarp, I use a groundsheet (but not with a tent) and just put my pad on it. Remove sharp rocks and sticks before doing that though. I rarely have fires, so I don't worry about fire trenches.
Tarping is more nuanced than tent camping, and is a bit more work, especially in inclement weather. The tradeoffs are a lighter pack weight (though some tarptents are encroaching on some of the heavier tarp weights) and more of a "connection" to your surroundings. In winter, I'd suggest having a tarp large enough to pin to the ground and still provides ample space to move around under. This is why I use the Trailstar. Many of the Mids are good for this as well, and some would argue better since they are a bit easier to pitch.