Welcome @bambeeboom! So happy to see another 3-roomer. I really envy the size of your bathrooms!
I did everything not in order either, seriously anyhow "BOM"! And I didn't have a theme in mind or colours. I could only come up with a set of criteria like easy to clean floors...no white lights... no plastic chairs etc.
But I think what helps is printing out a nice big floorplan of your place ( I used my company's A2 printer tee-hee) and Blue-tack a few somewhere you always walk by. Sometimes while I'm putting on my make-up an idea will strike me and I will quickly reach over and mark it out on the floorplan. Once you settled on what you want appearing in your house (be it to knock down a wall or put up a built-in, or even a moveable table/ sofa/ cabinet), you can start making a list of must-haves. That will be your groundwork for your ID/contractor. Other things that helped me were pictures of homes or parts of houses that inspired me (E.g. my subway walls from Pinterest). I'm sure you will have things that you die-die must have.
trcd is right in that ID charges for designing fees, and contractors usually don't. Both have their pros and cons. I'd expect the ID to be the project manager and for contractors, I ended up pm-ing them 50% of the time as the main contractor was running between worksites. So far what I've seen from people on Renotalk is that if you know what you want already, a contractor is enough. But if you do not and you really need input on the design element, then go with an ID. With a contractor you are really relying on yourself, so you must have the confidence to know that the cabinet laminate colour you are choosing is something that will look good to you as a whole in the end. Having said that (sorry I am really long-winded), we are more forgiving with our own choices vs. those made by others for us.