First of all, I don't think you have to worry about the bike limiting your progression. Unless you're a Cat 1/2 racer, there's always more room for your fitness to grow versus fancier/lighter equipment.
I hope the LBS measured out your inner seam length when they put you on a 52 cm frame, because it's an important factor in determining frame size. (Two guys with the same height can have dramatically different inner seam lengths.)
If you have a couple of minutes and a measuring tape, do some measurements and punch them into a fit calculator like the one below. That will give you some things to think about when it comes to sizing.
Don't buy from a dealer you're not comfortable with. I don't know your mechanical aptitude, but you might be going in to the LBS quite a bit as a beginning road rider. Something to think about.
I know nothing about the geography in your area, but is the gearing going to be low enough? If not, consider asking the LBS to swap for a bigger cassette until you build up your power. A smooth spin is good, mashing is not great for your knees. Low gears are your friend.
"The song of a bird…We used to ask Ennesson to do bird calls. He could do them. How he could do them, and when he perished, along with him went all those birds…"-Return from the Stars, Stanislaw Lem
"We just walk around, and sometimes we go out and dance, and then we listen to the environment."-Ralf Hutter, Kraftwerk