Yes, there are some things I would not put in raised beds. All of my perennials are not in raised beds. Also, corn and potatoes. I am not sure what else. I have asked, but am not clear on what requires more depth than I have with 8" beds. Not even because my soil is below the top. I have wire that will let the roots go deeper, but the soil is clay below the bed so I doubt that most of my current crops will penetrate the clay.
You can put a bed in quickly. Don't make a major project out of it. Do one bed and you will see how to do it. If you use 2x wood, you will not need to brace it. Use wood screws, I used deck screws, three at each corner. You will need a level to get the bed set level. If you have critters that will attack from below, then you need to put poultry wire in the bottom.
When sizing the bed keep in mind you want to get to the center easily without climbing into the bed. You don't want to compress the soil. 4 foot wide seems to be the limit. The length is up to you, but I would make a small one to begin with. Maybe 4x3. Easy. I think most poultry netting is in 3ft rolls. I had to lay down two three foot sections. I am doing the compost the way Dorine suggested. It is working. So, by next fall I will have a supply to add to my beds. The worms are helping.