Do you know if I can go from version 1709 to 1903 directly without having to install intermediate versions?
Yes, this is possible using the MediaCreationTool or an Windows 10 1903 image or DVD.
When doing this installation, do I lose the configuration of users and / or programs?
The Windows Setup will preserve all your programs, settings and data.
But I would ALWAYS do a backup before performing the upgrade.
I think that I will not update the version of Windows 10, I will stay in version 1709.
Would it be possible to install the pending patches until April 2019 with Wsusoffline or another offline way?
I'd recommend you to upgrade to get the most recent security fixes. I'll provide you a list of links, if you tell me, whether you have a 32bit/x86 or 64bit/x64 system (if you're unsure check C:\Windows\wsusofflineupdate.log; there should be a line conatining the OS architecture).
Wer Rechtschreibfehler findet, darf sie behalten oder an den Meistbietenden versteigern. / Everybody finding a misspelling is allowed to keep or sell it.
aker
WSUS Offline Update „Community Edition“
https://gitlab.com/wsusoffline/wsusoffline/-/releases