Hi Al.
Welcome to this great forum, been very helpful for me since my bike rebuild last year, I live in Desford, so not to far away from you, any help please contact me. Some sound advice already given, don,t worry to much about the dynamo, its only there to support the lights, also battery condition not critical, as only requirement is for riding in day light is the stop light. You may require help with the mag, and there,s a good guy with small unit located in Narborough. The mag is the interface for the ignition (no battery involvement required). Supreme Motor,s in Earl Shilton stock most things, but I,ve found the internet is usually cheaper. Read up on key topics, all covered in much detail on this forum. Its so much easier these days to record disassembly and assembly via photos, and print almost any information off data sheets on the internet. A picture book or parts catalogue is very handy, but again you will find these to download.
Best of luck, but you have already had a bit by picking up a pretty original looking A7 for bargin price.