You can definitely blend them all together Elizabeth, but I’d add in a base note oil (and maybe even another middle note oil) if it were me to round the blend out a bit more. Those oils are very floral and light so I’d add a couple others in to bring it down some, but that’s just me. If you like that scent, you can just use those and that’s it. Especially if you’re using it as a spot treatment sort of thing.
You need a cool-air diffuser. These diffusers usually require a small amount of distilled water to be added along with essential oils. Note: Cold air diffusers ranges vary, with most around 250 feet. So if you are trying to diffuse your bedroom and living room, most likely you will need two diffusers. This one is my favorite for the money and size/features.