I'm not a medical student yet (still applying), but I've been married for 5.5 years and my wife is currently working on her doctorate, so I hope my two cents will be helpful.
@Matthew9Thirtyfive is 100% correct in that compromise needs to be the way that both life partners approach a marriage, particularly if you are both professionals. I am shaping the schools that I apply to based on the ability of my wife to complete her doctorate, while my wife will be ready to move wherever I get sent to when I am active duty (the military has given me the HPSP scholarship). We've also planned this around the feasibility of either of us being moveable (i.e. having finished our education programs) at a given time. If you take a "100% me" attitude (or your fiancé does), then this is a massive red flag; someone who isn't willing to make any compromise on their future to make a life with you isn't someone that I would advise trusting long-term.
However, more to your original question, I would highly suggest that you make compromises on your perfect wedding. It sounds like you really want to do the full wedding planning thing with family, a bunch of guests, and all the fixings. That takes 1) a lot of money, and 2) a
lot of time. I was incredibly lucky in that my wife (along with significant help from my mother and grandmother) did the vast majority of the planning for our wedding. Even though my wife was still finishing her undergraduate degree at the time (and therefore had quite a bit more free time than nowadays), it was still incredibly stressful for her, and this was when our wedding was very small, relatively non-traditional, and
extremely cheap (still costing around $10,000). I would think that you will have a very hard time putting in the planning for your dream wedding at any stage of either you or your fiancé's career in the next 6-ish years.
If I were you (and assuming that you are making a thoughtful decision and not rushing into a marriage), I think the best way to go would be to get married sooner than later; continually putting off a wedding, particularly for many years, can potentially breed resentment and frustration. Instead, I would suggest either doing a smaller, more intimate wedding (potentially where family helps with most of the food, location, photography, etc.), or do a destination wedding so that far less planning is involved. Name changing (if either of you are thinking of doing so) is probably also going to be easier if you do it sooner rather than once you actually start practicing medicine and get established professionally.
No matter what you do, remember that as
@Matthew9Thirtyfive also said, getting married isn't like having a child; people often asked my wife and I about it (since we were quite young at the time), but the thing they didn't realize is that the only thing that changed is that we gained a lifelong partner that we knew we could count on (plus all the legal benefits). Don't let your careers discourage you from getting married. People like to make jokes about marriage, but marrying my wife was unquestioningly the single best thing that happened to me in my 20's (I was 24 when we married) and, without her support and our ability to work together on emotional support, finances, or logistics, I wouldn't have been able to join the military, become a paramedic, or apply to medical school, all things that are incredibly important to me and have changed my life for the better.
