I think it will be a rush to plan a full-blown ceremony in four months.
Why not postpone for twelve months, which will give you plenty of time to sort things out?
Or, and i think this is more likely, you really don;t want to get into the serious hassle of planning a wedding, no matter when it takes place, then you need to have a serious talk with your partner.
The wedding is like the marriage - it's about the two of you, and starting off married life with an event you clearly don't want is not the best start for anyone.
If your partner is so keen for all the circus that goes on - let him do the organising, and you will just turn up - a role reversal if ever there was one!
Better would be for you to have a serious talk about it. Explain how you feel, and if he is the right man for you, and I am sure he is, he is going to understand that having his way by putting this pressure on you is not the way to show your love for the woman you are spending the rest of your life with.
If he digs his heels in, and insists on having a big wedding, against your wishes, then you should look seriously at whether you should be going ahead at all. If you disagree fundamentally before you are married, then you will continue to do so afterwards.
Hope you get it sorted - please let us know.