Well it's going to be hard unless you know what plants you have to start with. I assume you must have recently moved to this property. If it were me I'd wait to see what blooms and figure out what you like. Or, you could probably find a local master gardener or someone who can identify plants who would be willing to come over and offer some advice and help you identify what you have. I think you also need to decide what you truly want. If this space is too big, decide how large you want it and then figure out how to shrink it and what plants should be included. I'm sure you have some wonderful plants already in place so I would not start over, but again, you may need to get someone there to help you sort it out. Or, let it go this summer and take photos through the growing season and attack it once you know what it looks like and what plants and colors you own.