You'll be spoiled for choice really, in a SE-facing garden. If you can bear to wait, I'd live there for a year, so you can go through the seasons, to see if anything new pops up in spring / summer, eg bulbs, or perennials like hollyhocks, verbena etc, and which are the dry or soggy areas of the garden. Meantime, you could just put in some fast-growing annual seeds for some summer colour, say Morning glory if you want a quick climber to cover something over, or super-simple daisies, poppies, cornflowers and so on.
If you want to get going, start by thinking about how you want to use it, eg, grow vegetables, somewhere for children to play, an area for compost etc - or just simple with borders and a lawn. Then, consider the view down to the end of the garden from your house - is there anything you want to hide? Or draw attention to? Think about vertical height, eg putting in a small tree (www.gardenersworld.com/plants/features/structural/trees-for-small-gardens/1116.html - has a good list of trees which have year-round interest), and using that as a focal point / to work around.
If you're going to put in borders, make them bold! Wider than you think, and curvy if you can - not much about nature is straight.
There are so many beautiful shrubs and plants, it's really down to personal choice. I love the massive hydrangea Annabelle, erigeron daisies which self-seed like mad, ditto tall purple verbena bonariensis. I like planting spring bulbs in grass too - so easy, and they look lovely when they bloom.