Yes. The file dotNetFx45_Full_x86_x64.exe works on both 32-bit (x86) and 64-bit (x64) systems.
If you are running a 32-bit version of Windows 7 and need to install or repair Microsoft .NET Framework 4.5 without an active internet connection, you need the offline (standalone) installer .
No, but .NET 4.5 is an in-place upgrade that replaces 4.0. You do not need 4.0 installed first.