Awww Hubnubs, i can totally relate to your height dilemma lol because im 5’1 and my fiance - to be is 5’10!! Also i’ll be the bari bahu once were married aswell inshallah.. and wait for it..im also brit-born and hes born and bred in Pk!! im sure u make an amazing couple and all these worries will fade away when you’re there and actually living as his wife, inshallah 
i think you can only prepare yourself so much for this situation, because at the end of the day you cant really be fully prepped for something you’ve never encountered before(ie getting married and the issues that come with it), its going to be a whole new experience but just have faith and do dua that your marriage is blessed with alot of love and understanding! ooh and as for wearing flats..i used to feel really self conscious at fist about the height difference but now im used to it and wear what i want to..besides girls look the best in heels 
lol sorry for the essay hun, just had to share! xx