Trying I agree with others on here, certainly ditch wedding favours. What are they even for? Who cares?
Also car to wedding - we paid £350 (19 years ago!!) for a fancy vintage car and nobody saw it. I would have ditched that in hindsight. Do you have a long way to go from church to reception? Even if you do, can someone with a smart motor (big Merc or BMW or even just any nice colour, shiny metallic saloon) drive you?
I would also very much not bother with stationery - again, we had Orders of Service printed and what a waste that was. Check with the church but I bet they can provide hymnbooks or even have facility to project the hymns - which is the only bit anyone needs to see really. The fact that your mate Jemma is reading Shakespeare's sonnet will be obvious when she steps up to the lecturn.
£300 seems a lot for a wedding cake but maybe I am out of touch. Last wedding I went to the bridegroom made the cake. It was fine.
I agree 7 ushers etc is not needed. We had a church wedding and we had a best man and one usher. Both wore smart suits (their own)
I would expect the reception venue to make itself look nice if I were paying £60-70 a head. I am not a fan of all that wedding glitter confetti stuff anyway.
And yes, get your hair done for sure, but everyone else can do their own, ditto make up. Make sure you don't go for pale pale colours for you or you might look washed out.