The best condition for storing seeds is the opposite of what they need to germinate - that means dry, and cool. I'd take them out of your garage where humidity and temperatures must surely fluctuate. An inside closet or drawer will be more stable. Mine are usually in my desk, right now since we've moved in the last months, they are in a drawer in a guest room :) The humidity in my house is generally low, if yours is higher you might want to consider storing dry, in your refrigerator.

To buy commercial seeds and be assured of fresh seeds for next year, you need to be patient and wait for this years harvest to be processed, packaged. When the catalogs and websites have their 2014 offerings listed, order. Unfortunately that's often right about the time we can be busy with things other than gardening on our minds, Dec/Jan for some...

Are you saying you shouldn't use seeds from the previous season and always buy fresh?

No, although you could have a problem with good germination from some seeds if you've had them in your warm garage. It's fine to keep seeds from year to year, depending on which seed, a few types are not good held over under any circumstances and the package will usually say something along the lines of 'short viable'. Onion, parsley, delphinium are examples of seeds you may not want to store...

You asked when to start acquiring new seeds to fill your wish list, and to that I answer Not now, because you will be getting seeds packaged last season, wait until right around the holidays when the new harvest will be available. If you are buying new, you may as well begin with the freshest.