Hello Tim,
I've been doing exactly what your planning. My lawn has all but gone, in it's place are differenting heights, walls and large planting spaces/beds.
I want a true cottage garden with different heights of plants, eventually I want to be able to walk through my garden, which is good for bees, insects and all wildlife.
I would grow the plants that you like, rather than follow any other persons sense of planting. I'm growing a lot of perinnial plants which won't give me a show til next year but I've got some annuals on the go a well.
I agree thought that mass planting of one plant is best for the overall effect. I wanted snapdragons in my garden at the beginning of the year so I grew them from seed................ I've still got loads,even though I gave loads away. I've filled my new beds with them. Looking forward to them flowering but it might not be the same next year.
My advice is just go with what you like and work around what you have already.You can always change it. Gardens are never "right" and never complete