I'm not a fan of wallpaper, though I'll admit there are some powder rooms on Houzz with beautiful, two-tone wallpaper that I love. The last time we bought a house we had to choose between two equally desirable, quite similar vintage houses--one with wallpaper on every wall (even in the hallways!) and one with painted walls throughout. In both cases we planned to repaint in colors of our choice, but we bought the house without the wallpaper because it was simply less work to repaint the painted walls than to strip a house full of someone else's tacky, outdated wallpaper. So by all means use wallpaper if you love it and will be in the home for awhile, but don't expect anyone else to appreciate it when you sell. Wallpaper (like patterned fabric) is just too individual a preference to translate easily into someone else's aesthetic.

As I said before keeping clutter under control is the key, get lots of storage ,you said cost is I s an issue. Look at IKEA they have solutions for wall units that you can get in different colours and that in itself will brighten the place. You would benefit from a buffet next to the kitchen /dining area or a large wall unit with lots of shelfs and drawers, coffee table with storage drawers , storage unit with baskets for kids toys and school stuff, once you have this under control start adding rugs if think you still need it. By the look of it you have small kids get them to put things in appropriate place and get some funky coat hangers in the entrance so they can hang hats and bags etc.

That isn’t the one I had in mind... BUT this one is even better! Thank you so much dreamer :))

Some comments, I hope they are helpful. Create a gravelled area for your fire pit. Laying a some sand, levelling off, a weed barrier and raking gravel is within the skill set of most handy people. Use treated timber for an edging to keep it neat. Buy a nice ready made steel fire pit. Buy some seating. Your planting lacks a scheme. Without a scheme your yard will not look put together the way professional landscaping does. Every plant has to be chosen for a purpose (texture, height, colour, privacy etc). You also have all your garden beds in a perimeter against the fence. That's fine for a starting point. But to make the place look inviting you need some garden beds in the yard too. Please avoid the common habit of putting shrubs in the middle of the lawn. It doesn't work well and also makes maintaining your lawn difficult. If you want to make say the entertaining area private from the kids play area a full garden bed is usually a better bet than just a shrub or two. By putting multiple shrubs of varying heights and a creeper in a larger section you create outdoor zones and properly define the area. What you really need to do is measure your yard, draw in your house and all paths and then start drawing in the entertaining area, the kids play area, the veggie patch etc. You will probably have to play around with the layout for a while to come up with something you like and works. Trust me, doing this first will save you a lot off $$ on plantings that don't work and you want to remove later. When you create garden beds do it with three heights. So something under 6" tall, something under 2ft tall and then something over 3ft. Not a definite rule but a good rule of thumb. By having multiple levels in your garden beds you create a more impactful and interesting garden. When gardens are meh, its usually because all the plantings are the same height and it looks flat. Take a look at these gardens to see what I mean.... Alright this fire pit is obviously professionally done, but what you need to look at is how the fire pit is clearly separated from the rest of the yard. The seating creates an outdoor room feel. But also if you look behind the seating there is also a large garden bed behind it. Although the scheme isn't finished my bet is that some tall screening plants are likely to be planted there to create a more intimate mood and shade from summer sun. Having garden beds define a feature really works. This is what I mean about having layers in your garden beds. If this yard was just a row of trees along the fence and then say a low hedge in this front bed it would look okay but not great. They have used different colours, textures and heights all in the same bed here to create something much more interesting. The planters in that corner also create height with the strappy plants. This is why you need to plan our your whole garden so you know that all the plants across the yard work together coherently.