First thing, you definitely did not pay over the odds - the advice, fitting and expertise to be gained from going to a proper dealer makes it the best value place to get your stereo stuff. Walk in there with an internet purchased unit and see how much they want to fit it........
I was / am an SQ boy, with a slight addiction to bass when on the move! I was running an Alpine headunit / EQ set-up, PG line drivers, JL amps, speakers and sub, all sorts of install tricks etc. Few trophies in the cabinet from it.
The Alpine stuff is really expandable. Even managed to get my steering wheel controls to work and the phone is controlled through the headunit.