Okay, from what I know about filters from 10 years of owning one for my fish tank:
Most 10"x2.5" (the most common household size) filter housings come with 1/4, 3/8 or 1/2. All for about the same price, between $15 and $20. Ebay has them cheaper than that. They do have both 20"x2.5" and 10x4.5" fatties both are rated for high flow, which you don't really need in most homebrew setups. Sure, you can get the high flow models, but you're more than doubling your price for setup and every filter change. Stick to the 10"x2.5" filters, they're easier to find and cheaper too.
Most housings have places for screws on top. You don't have to pay for a $5 bracket when a $1 angle bracket will do.
If you get a 2 housing setup, your carbon block will last longer. A $2 5 or 10 micron filter will drastically improve the life of your $15 carbon block filter. If you figure it will cost you about $25 for the extra filter housing and filter, you easily make that back after the second time you'd change your carbon.
Juvinous has the best solution for somewhere you can't get to a pipe (or you rent.) Get a dishwasher/icemaker connection and plumb from that. I especially dig the flexible hose from the shutoff to the filter. Brilliant idea. Just remember that if you end up with a 1/4" valve, that's going to be the restriction on your flow. You might have to search one out that's bigger than 3/8. I'm used to NYC Home Depots, so your selection might be much better.
If you have the space and the inclination, you can go with a three filter and add DI. Then your water will be almost free from anything, basically clean H20. You can build the exact water profile you want. However, to get the most out of your DI you need to slow it down to probably under 10 gallons an hour. If you're doing 5 gallon batches, no biggie. But if you're trying to do 20, it sucks donkey balls waiting for the water. I just filled a 60 gallon aquarium and it took about a day and a half.
If you're going to go with DI, I HIGHLY suggest you go with bulk DI resin. I get about 200 gallons of 0 TDS (total dissolved solids) water per DI change. If you're buying throw-away carts, it's about $30 each. If you buy a refillable cart and bulk DI, it's about $6.
I get a bunch of my filter stuff from
www.buckeyefieldsupply.com They have just about everything you need.
I do get my bulk resin from
www.resindepot.com
B