Newspapers are fine, but if you want to kill brambles and grass, cardboard is better. But more important than cardboard vs newspapers, The secret to a good kill is to apply the mulch after growth has resumed. That way you push down the shoot, and you have a long time before the paper breaks down and lets perennials through.
There are plants that like degrading mulch, most notably tomatoes, garlic, potatoes, squash. Degrading mulch tends to be acidic, but not all the time, and not necessarily low nitrogen unless you use very brown materials. Lettuce, for example, is sensitive to acidity, but it will be very happy if planted directly through six month old leaves mixed with some manure. In practice I always give wood ash to just about anything i grow except potatoes (I have acid soil, and I prefer wood chips, the most acid mulch of all, because I plant most everything in seedling form).
Over time the pH of the degrading mulch climbs up to near neutral values as it becomes soil. It will start to look like soil. There are tricks that you can play. First, if you use leaves as mulch, they will be 99% gone by next year, with a decent pH, so you can seed directly in the resulting soil. If you use chunkier mulch, like wood chips, you will have weed protection for two years or more, but you will have to plant through the chips until they are gone. Wood chips start quite low in pH but when they are done their soil is similar to that made of other mulches, if possible with a stronger humus. If you use cardboard covered with leaves or mulch, the cardboard is 99% gone the next year. if your mulch is not quite done, and you want to seed directly there, gently rake it to one side of the bed. Use that side for potatoes or garlic, and the raked part for carrots and beets. The raked part will have more weed seeds than if you had not raked it, but still less than the soil underneath it.