Hi Calin, I have quite a few raised beds for my semps so I'll try to answer some of your questions.
-If yours are just going to be temporary, I think wood would work fine. It takes many years before it deteriorates. Cedar is always a good choice as it does well out in the elements.
-I do put a liner in my beds - to keep the soil in. I've noticed that even if the beds seem to sit flat on the ground, somehow the soil seems to find that one little area that is lower and over the years it seeps out some. Again, if your beds are only temporary, it might not be necessary for you. I use a heavy weed barrier fabric for my liner. Some people put chicken wire on the bottom to discourage critters from digging up under the beds.
-I mix my own soil for the beds as I don't think my garden soil has good enough drainage for raised beds. I use garden soil mixed with chicken grit and leaf compost. Whatever you use, make sure it has good drainage. Chicken grit is a small stone with sharper edges, it's not a rounded stone. I think that helps with drainage.
-If you want to sell your plants in hypertufa pots, it really doesn't make any difference if you use plants that you've grown in the ground or in a container. Either will do great. I have many hypertufa pots and unless it's crazy hot out, they usually only get watered once a week anyway. So yours should be fine if left alone for 2-3 days without water.
-If you're worried about weeds coming up in your raised beds, you can always line them with newspaper or sheets cardboard. Or maybe even place layers of paper/cardboard over the area for several weeks before you build your raised beds. That should kill any vegetation under them.
-Bev had good answers for your seedlings
Good luck with your new projects!
