1) Sony Alpha mount lenses can't be put on Nikon bodies. Nikon lenses can be put on Sony bodies using an adapter as Nikon's flange distance is slightly longer than Sony's. Other issues with using a lens adapter:
- only manual focus
- lens data will not be sent to the camera as the electrical connections will not be compatible
- unless you have lenses pre-dating the new Nikon 'G' series, you won't be able to easily set the aperture. I think all current Sony Alpha lenses do not come with an aperture ring. Neither does Canon or Nikon G series.
2) For portraits I usually use these range of lenses
- a general focal range between 70-150mm is good for portraits of individual people and small groups, this is what most photographers use
- On special circumstances an ultra wide focal length range between 15mm-28mm if I want to get really close to my subject and have some distortion effects
(try to understand the expansion effect of wide angle lenses and compression effect of long focal length lenses)
- mid focal length range of 35mm-80mm is useful for group portraits.
3) for landscape, I will use a focal length that would be suitable for what I want to do
- single shot wide image I will go for an ultra wide lens (14mm-28mm range)
- for panorama I use a 50mm lens, I use prime lenses for this. If I remember correctly 50mm is considered close to what our eyes see.
- and don't blacklisted_site using a telephoto lens for landscape, there are times when you may want to zoom in onto some distant object.
So having said them, consider what you want to do and try to find lenses that are within your budget. I use to own a Sony A-350 for about a month and with that body I had these 2 lenses:
Sony 18-70mm kit lens (about 80GBP used), not sure if Sony still produces this lens
Sony 75-300 lens (about 180GBP)
an alternative is the Sigma 70-300mm range lens for about 150GBP
You can also get the Sony 18-250 lens that covers a long focal range, one single lens instead of having 2 lenses.
I would also recommend getting at least a 50mm prime lens, the advantage is wider aperture, small compact size, low price and usually better optics than zoom lenses.
You will have to try the lenses out at a store, do some research, find reviews, etc as I'm not a big fan of Sony cameras. I bought a Nikon one month after I bought the A-350 which I sold to a friend.