There are differences in watercolor paper qualities in how much paint they can hold, how soft or hard the surface is, how they handle layers, what the surface textures are, archival materials and so on. I recommend 140 lb. (300 gsm.) or heavier weight paper.
For students I recommend a 9 x 12 inches pad of paper to experiment with. Student grade is fine, however, I don't recommend Strathmore watercolor paper. It is difficult to handle, can pill easily, and even the professional grade has difficulty in receiving multiple layers without getting overworked. Look for several brands for students such as Canson and Grumbacher.
I use mainly professional papers due to their handling and surface qualities. I use Arches Cold-Press Natural White sheets, ordering 5 or 10 at a time, 22 x 30 inches standard size, cutting them down if I need to do smaller work. With larger work, I use 25.5 x 40 inches, or 29.5 x 41 inches, 300 lb. weight. I occasionally use Canson professional papers, the 100% Cotton Cold Press with a deckle edge. I have used handmade Indian Village paper, however, it's no longer available. Currently Shizen Paper, also handmade in India, is a good substitute.