Good tips on here so far. My two cents:
- Shoes: I agree that most people do best buying shoes in person. You will want to decide whether you want shoes you can walk in (MTB/touring style; two bolt) or pure road shoes (stiffer, not fun for walking; three bolt). Most shoes are going to be compatible with one system but not the other.
- Pedals: Just make sure they're compatible with your shoes (two bolt or three bolt systems). Pedals are easy to install and you can find deals online, though it's not a bad idea to have some grease on hand for greasing the threads.
- Jerseys: What is your preferred fit? Many jerseys come in different cuts, with labels like 'club' (looser, relaxed fit), 'race' (tight fit), and 'pro' or 'aero' (skin tight fit, like a second skin). Tighter jerseys also tend to have features that keep them from moving around, like silicone grippers. Sizing is more forgiving in looser jerseys. Cycling apparel in general runs smaller than American sizing, especially with non-American brands (incidentally, this is also true for non-American brands of street clothes.) I've personally not had a problem buying jerseys online...but it requires reading a size chart with measurements in cm and making good decisions, knowing that I might wear a medium cycling jersey even though my favorite band T-shirt is an XS.
- Shorts: Like others, I recommend giving bibs a go. You probably will not develop a preference for chamois/padding until you get some miles in, and your preferences may change over time. I personally recommend not going cheap. If you buy online, same deal as for jerseys (non-American brands use non-American sizing), and a good return policy is helpful.
As others have mentioned, other gear you should probably get includes:
- Front/rear lights, even just for daytime visibility
- Floor pump with PSI measurement
- Equipment for fixing a flat and a place to store it on the bike or in your jersey
- Eye protection (dragonfly to the face at 40MPH is not a good time)
- Arm sleeves and/or a wind jacket, assuming you are in Wisconsin
