G-10 50x90 1 kanal renovation

Can someone give me guidelines on what to look at when renovating a 20 year old house? the house is 50x90 , and I’m looking at redoing all bathrooms, kitchens, floors and potentially plumbing. What are some of the do’s and don’t? Also any reputable renovation companies? What would be a realistic budget considering the above main areas of renovations. Thanks