Not even a tripod is really necessary based on your explanation, though I'm assuming that using one makes alignment of images in postprocessing much easier
The alignment is not a consideration in praxis. The tripod is
necessary (in conjunction with a pano braket) to avoid parallax errors. This becomes an issue in short distances (for example indoor), or if short and close objects appear in several frames. This is too complex to describe in short.
Another consideration is cropping. If you have a tripod and you levelled it, you can frame better than hand-held. I shot at least the half of my panos hand-held, and sometimes I made errors. Example: Devil's Garden in Utah. was standing on top of one of the hoodoos and shooting a wide, single row scenery, about 265°. The result is this:
I had to crop away a large part of it. When shooting wide sceneries hand-held, I swing back and forth several times looking through the viewfinder before clicking, to judge the correct hight and to avoid being led by the scenery, but this time I did not (honestly, the top of that hoodoo was not a prime place for shooting, but I needed the height).
Two more notes:
1. At the beginning you should shoot only with fixed exposure. Preparing the image frames before stitching can be very tedious, practical only in raw, and required only in few cases, namely when the dynamic range of the scenery far exceeds that of the camera.
2. There is no basis to think of a single prime lens. I suggest you to start out with a very good, wider zoom, like the Nikkor 17-35mm; you will need another one, like 24-70mm. I find the snobbish attitude tireing, that you frame better using a prime. I have used primes for pano, 20mm, 50mm, 85mm, 200mm, but often I needed the zoom. Particularly when shooting pano, one does not have the freedom to "walk to the right place" with the prime, because I need to stay on a spot, from where the
entire wide and/or tall scenery can be shot. The snobs reiterating that rubbish have never shot anything from an outcropping on a steep hill or standing on a small rock in water. To avoid losses due to cropping, the field of view needs to be selected as it fits best for that scenery from that position.
