Hi!
First, you won't find much re: shopping online in Costa Rica. Most people find places by word-of-mouth. There are a few large stores (chains), but so much more can be done in the one-of places in each city.
Some chains: Hypermas (household supplies), Pali (groceries and some housewares), Automercado (high-end groceries), Pricesmart (housewares), EPA (like home depot). These are almost all centered around San Jose.
Forget Target, etc, and explore the smaller stores in your town-to-be.
There are plenty of clothing stores - malls are congested with them, and there are many in the central areas of the cities (Llobet's in Alajuela centro, for example, is just a block from the central park, and is itself a landmark for directions).
One of the best things you can do is to talk to your neighbors - they can tell you where to find anything! (shoe repair, linens, freshest produce and meat, seamstress).
Ants - don't leave food out for long, sprinkle boric acid around, spray w/ Cynoff (avail at agro business stores), encourage geckos.
Emergencies - dial 911 
Bomberos (firemen) usually take care of snakes (and bee hives)
salons - oh boy! Hair and nails are a big deal here! Even in small towns, there are people who do manicures (often out of their homes), and several beauty salons! Most local women have regular manicures and pedicures.
Bedding - it is difficult to find sheets w/ high threadcount. If this is important to you, bring them. Likewise, down pillows. Sheets and towels are expensive. ($100 got me 2 twin sets and 3 bath towels). You can look here: for ideas of what is available.
jobs - you can't legally work unless you have either (1) a work visa, usually arranged before you come or (2) permanent residency, usually not available until after 3 years of temporary residency. If you own a business, you can "manage" it, but not draw a salary.
We have yet to drive in Costa Rica. The public transportation system is great! (and I come from California, so was not used to thinking this way at all!) People usually shop for groceries more often, and buy less at once. However, when we bought a lot, we usually would walk to the store, then take a taxi back. Many have the little carts that hold groceries coming home.
Some places to check out for more info:
(also check the forum there)
yahoo's CostaRicaLiving group
feel free to read my blog - I tried to capture daily life:
JulieAndRickInCostaRica.blogspot.com