The program will not need to analyze the tracks again. All of that info is stored in the library database, which is shared between the two computers.
For your third and fourth machines there are a number of ways to handle them. You can simply transfer the files from your NAS and use a library backup (in conjunction with the
Rename, Move, and Copy tool) to transfer the MC library. You can also use the handheld sync tool within MC to transfer any new tracks to the computers, and although this is a bit more elaborate initially it is less time consuming once set up.
If you truly want to go with option 1 (option 2 is recommended), then:
1. Create a backup of the MC library (File>Library>Back Up Library)
2. Create a new library (File>Library>library Manager>Add Library)
3. Choose local library and select a path that resides on the NAS where you want to keep the database
4. Once the new library is loaded, restore the backup (File>Library>Restore Library)--this will recreate your old library on the NAS
5. On computer 2, create a new library and browse to the same directory you chose to store the new library in step 3.
6. Computer 2 will now have read-only access to the library and computer 1 will have read/write access
If you ever want to set it up so that both computers can edit the library then use Library Server.