For me, i think it is best to follow the ones who followed you because in business, you need to get a lot of friends in your promotion.
Yes, You Can always follow your follower, otherwise they unfollow you after some time. If You are follow your follower then they don't unfollow you. Also its help to generate new followers because your see to all followers of your follower.
Its not necessary but it does help in gaining other followers i.e. people who follow your followers will be inclined to follow you. However I would never automatically follow as you need to filter out any spam followers and not reciprocate, but block and report if necessary.
this is a very good sentence "Following our follow our followers is brilliant" because i do not understand what does it mean ? if you are a famous man or women then lot of people will follow you and you will never need to follow them