There are lots of Tiagra and some 105 bikes in your range. My pick would be something like the very well rated Cannondale CAAD8 series. The Tiagra model is around your budget, but I like the 105 5 which may be in your budget on sale. Especially since you are just starting out, and you want to do long rides, a higher stem is probably in order.

This is just one suggestion for a bike that will carry you on long day rides at a quick pace, including your supported tour. You really have to do some research, some soul searching as to what you really want to do, and see what bike speaks to you.