Beneficial for you is entirely up to you. You have to have an interest in CNC to really leverage it as it takes some time to master. If you are talking about a business here then I would have to say CNC is a requirement. Hobby wise it really is up to you.
As far as building or buying there are so many designs out there that nobody can say for sure which is best for you. You need to address this yourself based on available space, interests, costs and your ability to acquire the required skills.
I'm not even convinced a CNC router would beal that useful for some of the things you list. They are great for signs that is for sure, but one off book shelves and the like I'm not convinced.I will be making signs, wooded boxes, bookshelves, and other things. I am sure my wife will have her list of things for me to make also....
Draftsight might be a good free starter for CADI am not sure on my CAD and CAM software yet so if anyone recommends something that would be great also.
No problem! I'm not sure if I was helpful here. As noted it is easy for a business to justify various CNC machines, as an individual it is a want more than anything. My suggestion would be to study up before even thinking about buying a machine. A CNC machine can make a good table saw look cheap depending upon what you buy and what you need.Thanks in advance
Joe