First thing I would do would be to round off those corner borders by at least a metre and a bit from the corner of the fence into the lawn. That would give you a decent sized and deeper border so you have the chance to grow things at different heights, it will also make your garden seem bigger by disguising the boundaries and those sharp edges . If you don’t you run the risk of having all your plants in line like soldiers because your current borders are narrow, might be worth widening them a bit too if you can. You have a great opportunity to make a beautiful garden, but don’t feel you have to do it all at once, gardens take time, but if you fancy for example, having a small tree like a crab apple then the sooner you get them and get them growing the better.
Next thing would be to have a look online at “yellow book scheme” this is a charity, people open their gardens to the public for a small charge . It means you can visit local gardens, see what grows well, find out which plants you like the look of, ask experienced gardeners for advice, possibly buy reasonable plants from them and with any luck eat some home made cake. Take a notebook.
We are coming up to autumn which is a good time to be planting a few shrubs, don’t be tempted to plant them too close to each other, if you plant things this year they will probably double in size by next year. Remember you have to fit in spring bulbs and summer flowering perennials and annuals as well!
I wouldn’t get anyone else in to plant for you, you will look after things much better if you have invested your own time in choosing, buying and planting them. And it’s more fun to do it yourself.