Interesting choice -- modern in lots of ways, but also mixture of classic and some retro stuff.
Blue would be a great way to add life, and I like the bright pinkish/purple but you would only want that as pops and not as a main color because it would get tiresome.
One thing that I find makes it easy to pull a room together is to go to a good quality print store (not poster store) and find something that you like the overall look of and the colors in -- this can set a tone for the room.
For example, you want something modern but not over the top and you want want some blues greens and pinkish/purples. Get a print that you like (usually about $100 bucks unframed.)
Get throws at Target, HomeGoods, etc. in colors you like. (Again, things that are washable and can also add pops of color). Yet pillows and make pillows (I have made these so that I can take covers off and wash them, just leave one seam partially open and close with velcro.) You can get quality fabric in small amounts (check remants) or decent fabric at inexpensive prices at discount fabric stores.
If you can get new chairs, try to get them in blue. Microfiber is good, and it looks like the blue furniture (except for the dining chairs) are microfiber; other stuff is high end upholstery cloth. Not the best choice for toddlers and babies, wait a few years). Microfiber is very easy to clean, doesn't stain and water doesn't hurt it.
The little bits of green in the thing that looks like an artwork made out of glass tile is also nice, and something you probably could do on your own after the baby (not until then, the fumes aren't good for you). Might be a nice way to relax during the very rare moments you get to yourself once the baby is born.
Just stay away from heavy accessories on the floor or with in reach. You could put up some high or staggered floating shelves and add some sculptures or vases and gradually collect; both top quality and knock-offs abound online.
Finally, very thing doesn't have to be done at once. Just buy stuff you like and keep adding when time and budget permits. Remember though: see the chairs in your photo: you can get nice stuff now if you can afford it, but cover them with relatively inexpensive "skirts" (not tacky, you can buy them or have them custom made) that are washable. Or, buy good bones for the dining room chairs and have uphostered now with durable material for kids; you can upgrade them with the nice brocade fabrics later.
Good luck with the design, and more importantly, good luck to you and your expanding family!