Man, you "surprise people." I'll never understand liking surprises; I'm a man who would gladly read a book that laid out everything I'm going to do from now until I inevitably reach immortality and become king of the energy beings (spoiler alert!).
My wife is a surprise person. In point of fact, my first attempt to propose to her (at the end of a play I produced and acted in, in front of our classmates and friends and all that good stuff) had to be totally abandoned because she figured it out and "ruined the surprise."
Naturally, I got her back by proposing at Chuck E. Cheese with no one to witness it but a surly teen in a rat costume.
So please know that if he is planning on proposing, he's probably trying his damnedest not to leak the information. It's not his fault he fails at relationship espionage; they don't teach that part in The Game.
In fact, he may just be feeling out your preferences, with the idea of using them if and when he EVENTUALLY proposes, many years from now. See? Didn't I just kill the excitement a little bit?
Hell, maybe he's pumping you for information because he's going to propose to his mistress! How's THAT for casting doubts on the whole situation? Take a deep breath, remain calm, and remember that life is a flowing river, a continuing journey where whatever happens happens, and you should just enjoy the passing scenery.
Whatever you do, try not to get too upset if he fails to fulfill your imagined expectations. Whether you get engaged tomorrow or next year, it sounds like he likes you a whole lot and there's nothing worse than two nice people getting upset because of something they thought the other one was thinking.