I’d recommend that you buy yourself another two external drives with a capacity of at least 1TB each. Use your 500GB drive with Time Machine to back up your Mac and all the files on it with the exception of your photos. Time Machine is a great hassle free feature that works great. You should also store your important documents on an online service such as iCloud, OneDrive or Dropbox to mitigate against theft or disaster such as fire or flood. Use the two new drives to backup your photos using Lightroom. Do an identical backup to each drive, keep one at home and give the other one to a mate for safekeeping in case of theft or disaster and swap periodically.
Thankfully I have the fast 50 taken care of via a new FD f/1.4. That lens was immaculate when delivered, it actually looked new. Going on your advice and bit more research and pricing I think I may go with the FDn 35-105 f/3.5 Macro, given the option of using this for macro work and the useful zoom range I think this could be a good fit for me.