18 mile trips are reasonably short, and 2200 miles a year isn't much.
General advice: You want to replace things as they break/get worn down. For example, if your chain is worn or cassette is worn, you'll want to replace it (though you should get several thousand miles out of each, but YMMV with riding conditions, maintenance, etc.), when the chain is properly lubricated. Make sure to do the 1 month service after you buy the bike (this should have been included with your purchase), since they'll have to adjust things (cable stretch, etc.). You can find most of the things you need to do for bike maintenance on Sheldon Brown's site, and you can look at books like "The Bicycling Guide to Complete Bicycle Maintenance & Repair" by Todd Downs, which goes over several common problems and solutions and adjustments.
Things you will probably have to adjust within the first year are the brakes as the pads wear down (rate is highly depending on riding conditions), chain cleaning / lubrication (and possibly a new chain at the end of the year), and fine derailleur adjustments due to cable stretch. You'll probably also have to clean the rims at some point due to residue from the brake pads. And you'll probably want to tighten nuts and bolts periodically, since they do come loose eventually. And you obviously need to keep your tires inflated properly (and possibly repair any punctures).
Bike Fit: The only things you want to replace off the bat are things related to bike fit (these would have come up if you had a professional bike fitting done). For example, if the stem is too long, you'd have swapped it out for a shorter one, or if the saddle is too narrow, you'd have put in a wider one. But, if you're properly adjusted to this, then you don't really need to replace things (but there is a great deal of personal preference to bike fitting - it isn't a science). One thing to note is that a wide cushy saddle isn't really good for anything longer than 5-10 mile rides for most people, so if you're not used to using your sit bones, a good saddle may not feel good at first.
Some accessories you may want: You may also want to go with some grips with bar ends like the Ergon GP3 which give you another hand position or so, for longer rides (you won't really need them for ~25 mile rides, but I do like them a lot, even for my commute). Even if you're not intending to ride at night, you should have some lights (cause you will get caught at night one day). You should also buy a helmet and a good u-lock. If you're commuting on this, you may want to get some full fenders - they'll keep crud out of the drive train and dirt off your back. A bike multitool is nice for rides as well, in case something goes wrong. A bike rack is also sometimes useful.
You should also be familiar with basic bike maintenance (like, how to change a tire, patch a flat, etc.).