Every shop will tell you wheels would be the first upgrade. Because if you plan on upgrading to a higher component set or frame, then a new bike is a better option since the prices are dropped to be included with the full bike package.

So if you think you'll be completely happy with 105 for a long time, then go for it and upgrade the wheels, otherwise think about spending a little more for slightly better stock wheels and a higher group set.

Enjoy it, whatever you get