There are many plants that aren't as finicky that can be considered good for beginners but more importantly each has a different lighting requirement. Can you provide more details on your setup?
All of my LFSs sell bunched plants, but I can't really think of any major advantages of bunched over potted or vice-versa.
The number of plants all depends on how dense of a planted feel you want and on the specific plants themselves as they all grow vertically/horizontally to different extents and their growth rates also vary. It also depends if you will have any driftwood or rocks as that will take up space where you can't place plants but will also provide spaces for certain plants to grow on.