Help creating screening and privacy in back garden

Hi all We are currently in the process of trying to sort our garden out. This will be our second summer here. When we moved in the garden was full of overgrown weed and covered with at least 6 tonnes of stones. The garden measures 18.6m x.10.45m and is East facing. And I think our soil type is clay. The property is semi detached with the neighbours house on the left. We also have another garden adjacent to ours at the bottom of the garden. The first 3.3m from the house will be paving. So we have 15.3m x 10.45m left. We are thinking of creating a lawn in the centre using grass seed. (We are on a budget so turf wasn't an option unfortunately) And I was thinking to leave a border of 60-100cm from the fence and the outside of the lawn for planting. Now the issue I have is there is a huge Mill directly overlooking our garden, directly opposite the rear of our house, about 500m away. (Very rough estimate) It has many large windows and I would like to create some privacy and try to hide the mill as much as possible as it's not pretty to look at. There is also a row of terraced houses behind our garden, with the bedroom windows of the first few houses overlooking our garden, starting with the house that has its garden adjacent to ours. These windows can also look in to my living room window which means I have to constantly keep my blinds partially closed. I would like to create a screening from these windows in the hope that we can use our garden this summer and I can let my children play without worrying and at the same time creating a permanent screen for my living room. My neighbour has a large tree along the boundary fence, about 12m from the house. It's a deciduous tree, so currently has leaves which is providing some screening for our living room from the row of terraced houses. However the garden is not screened by the tree. I would appreciate any help or advice. Please note I am a complete novice to gardening, so would like low maintenance methods. I also on a budget, so nothing too costly please. I was thinking of having an evergreen at the corner of the garden for screening from the houses at a height of about 3-5m. And some small deciduous trees or evergreens across the bottom for screening from the mill, at about 4-5m in height. I would like some colour in my garden and not just green trees. I have done some research on the Internet for the past few days and have looked at options such as clumping bamboo contained in pots, Ulmus Wredii Golden Elm for the corner of the garden and Photinia Red Robin, Amelanchier, Japanese Maple, Apple/Cherry Tree for across the bottom the bottom for screening from the mill. But there are so many different trees and bushes, I don't even know where to start. It's just mind boggling. At the same time I have been on an educational journey where I have learned names of many new trees that I never knew before! Many thanks in advance.