Yeah get the 105 brakes. Work better than Tiagra and look better too
Yes upgrade the wheels to something as bomb proof as you can get, it really makes a difference if they don't go out of true or break spokes. Just be aware some wheels (eg Mavic Ksyriums) can be very stiff which is good for racing but poor for comfort. Mavic Elites may be the ticket if they fit the upgrade budget. Don't go for something too deep-rimmed either. If you're riding recreationally you don't need something that's going to throw you around in the wind.
Who knows if zertz work or not. But they do last - my Allez Pro has them in the seat post and they still fill the hole ok. Not sure about the stay inserts but they're used a fair bit in the peloton and by riders around town, so it's safe to assume they'll last. Just not convinced on their efficacy
Remember to have a look at www.roadbikereview.com
for the wheels, bikes, bits etc you are considering buying. Useful reviews can be found there.