You can find all downloads in here https://support.fortinet.com/
I use only MSI for silent install, some of the switches that you can use are:
You can add features that u use only, using switch ADDLOCAL=
This switch will install group of features. For more details about features and levels look at attached screenshot.
Note that chosen level will install under levels as well.
For Silent install use /QN
For no restart use /NORESTART
There are a lot of other switches but this ones I find most useful.
Hope this will help