Generally rabbits should be kept in pairs so they have company as they are social animals. They need to be neutered to prevent breeding, prevent common health problems and make introductions go more smoothly. If you are home during the day and your rabbit is living inside with you then it may be possible to just keep one. Generally male/female pairs are easiest to bond but two males or two females are not impossible.
Baby rabbits are very cute but adopting an older rabbit has many benefits. When meeting an adult rabbit it is much easier to assess what personality they have, whether they like to be out exploring, sleeping or having cuddles and how they feel about interacting with people. An adult rabbit is also likely to be neutered by us where as with a baby you will have to arrange this yourself. Any teeth problems are also more likely to have become apparent in adult rabbit.