I have been using Brothers Keeper for about twenty years. I like it's simplicity. I would just say that if you are doing your own family tree as well as a one name study do keep them in separate sets of data. I didn't, and splitting the database later, as I wanted, was a bit trying. (Your descendants will probably be in both datafiles but that shouldn't be enough individuals to be a problem.)
Yes, you can shift the entire content of one program into another when you are ready. All the major family history programs, including Brother's Keeper and those you mention above, use 'gedcom' to transfer all or part of the database between programs. There are sometimes minor inconsistencies but it mostly works quite smoothly.