This whole house filter gets amazing reviews: http://www.lowes.com/pd_31217-43353-WHELJ1_4294822071%2B4294819817%2B4294821330__?productId=1082883&Ns=p_product_qty_sales_dollar|1&pl=1¤tURL=%3FNs%3Dp_product_qty_sales_dollar|1&facetInfo=Whole%20house|Complete%20system and is quite cheap compared to many other options.
Then my concern becomes whether I should put in a softener in addition. When I used a home water test kit, all the levels were high but well within safe levels, with the hardness being off the charts.
I've installed two water conditioners, and the ones in the "related items" column of your link are worth considering instead of the filter.
The Lowes product you linked is basically an activated charcoal filter. It's a really big one, and it backflushes to renew itself, but all it's designed to do is to filter out sediment and the odors. It won't help with dissolved minerals.
If you install a water conditioner (a water softener) instead of the filter, you'll get more for your money:
http://www.lowes.com/ProductDisplay?partNumber=416876-43353-WHES44&langId=-1&storeId=10151&productId=3824565&catalogId=10051&cmRelshp=rel&rel=nofollow&cId=PDIO1The ion-exchange resin will replace the calcium and magnesium minerals in the water with sodium ions that you can't taste or feel. (The water is soft enough to feel slippery.) The resin also provides a good bit of mechanical filtering and may eliminate the odor. Best of all, you can add Iron-Out powder to the container along with your 40-pound bags of salt.
It'll eliminate the mineral buildup in your piping, around your faucets, and on your toilets. Your sinks, toilets, and tubs will need less cleaning (and they'll clean more easily). You'll use a lot less soap, shampoo, dishwashing powder, and laundry detergent.
I second James' recommendation for a water conditioning company. They'll check the pH and let you know if you need to neutralize any acidity with a sodium hydroxide (lye) injection system, and whether you should also install a charcoal canister filter system. They'll be able to find a system that fits in your available space.
If you elect to skip the conditioners/filters then a much cheaper option for drinking water is a reverse osmosis purifier under your kitchen sink. But of course that just works for one faucet, not the whole house.
This whole house filter gets amazing reviews:
I'm no plumber. Are there 1001 reasons why putting a filter/softener in the attic would be a Really Bad Idea, or could that work? That seems to be where I could put this if I had to use more space. I can post pictures later, but at the moment the well comes into the house right into a kitchen cabinet with the tank (for pressure) right there without much space for anything else. No basement. Also, I'm on a septic tank in addition to well, no idea how all this will play with it. My research all seems to be contradictory.
It's a great idea... if you can guarantee that any leaks will go somewhere other than on the attic floor and then through the ceiling of the floor below. I've seen a lot of attic-mounted air-conditioning systems that eventually developed plugged condensate drains, so they drained to other (very damaging) locations.
I doubt that your attic has joists/trusses strong enough to support the weight of a filter/conditioner filled with water.
Oh, and as long as you don't live in an area that has earthquakes, hurricanes, or tornadoes!
The ion-exchange resin water conditioner plays well with septic tanks.