If you want low maintenance, plant in repeats. That way, you are pruning/deadheading/whatever once, which is better when you have limited time. Eg, say you decide on English lavender as something you like and is suitable for your garden, you cut it all back at the same time.
Think about height and not just what is happening at ground level.
If you go for evergreen shrubs, think about variegation to break the look up (eg a pittosporum Elizabeth, or a photinia Louise) and also flowering shrubs like lilac, weigela or camellia.
Something I learnt early on is not to go nuts at the garden centre so that you only buy what is in flower. When I started gardening, I spent hundreds in May, and my garden therefore always looks good in May and June. By July, it had all gone over, so I had to spend a fortune - again - on July/August/September flowering perennials and shrubs.
All gardens will suit a tree of some sort, a smaller one that changes by the seasons is an amelanchier. Trees give height and interest. Cherry blossoms and magnolias are also really popular. A small fruit tree?
An arch might be nice, leading to a small spot for peace and quiet. Climber growing up it, maybe? You could have runner beans growing up and around it and make that your veg patch?
Also if you’re putting in a play house, make sure you put a small bench or a seat for yourself. You’ll spend ages there supervising whilst they’re little, and it’s always nice to supervise in comfort.