Lovely house lovely garden.
I would leave at least four of the holly lollipops, they have mature trunks
That bring character and also their colour tones down the the lovely brickwork.
So you have six lollipops, my advice is to take out only two.
From left to right in the photo, number three, and number six. the (end one one the right)
The reduce the size of the balls, ( practice on the two your taking out)
To introduce a miniature acer.. your front door is central to the house
Your steps lead to a path going of to the right, to the left you have a bed
so if you extend that bed two slabs to to the left of your path, that's where
Your miniature acer can go (leaving the path intact of course!!)
Try and source a really nice sized one, and choose green.
If you would like a larger Japanese maple then place it further out in the lawn area, check out the views from your front window and place the maple where you can enjoy it most.
And for choice the lawn maple, for me would be, the variety Osakasuki.