How do I create yard of green space with fast growing trees & flowers?

Elm trees are known for growing fast and planting annuals already in bloom like petunias will get you immediate flower glory and joy. The petunias will spread out. We put down paper or weed paper and cypress mulch or cedar mulch around the plants (these 2 will not attract bugs like termites).

Just be aware that fast growing trees generally have weak/shallow root systems. That can be a problem in storms.

Don't know what gardening zone you're in. Lots of perennials bloom first season. Purple and white coneflower, rudbeckia. Hollyhocks and four o'clocks self-seed so they're around year after year. Be careful of ornamental grasses. Short ones tend to seed all over the place. Tall ones tend to fall over without some serious staking. For tall ones, I've used zebra grass ( miscanthus silberfeder). It stays erect though it may need some twine to help. It's green with a white stripe so it's not a pure green. It's well behaved. Only needs maintenance once a year in the spring when you need to cut the stalks down to within 1 foot of the ground. Which means you also have a winter interest plant. Doesn't self-seed all over the place.

Check with your local nursery, they will help with what does best in your area.

Check Michigan Bulb. They used to have fast growing trees. Pretty much a straight up and down kind of tree. If you need a hedge type plant to keep people out, try pyracantha. Not sure of spelling but they have a lot of thorns and have berries for the birds that turn red and orange in fall. Azalea is nice Be aware if you prune it must be just after they drop blooms. They set buds for next year as soon as all old blooms fall. Some evergreens grow fairly fast but needles on ground can be a mess. They make a good mulch but hard to keep any grass growing under the trees.