Resolution and scaling issues on dual monitor with nvidia (one 4k HiDPI, one VGA with converter)

I am trying Kubuntu 18.10 and I have a nvidia GTX 1060 (driver 418), a LG 27" 4k monitor (27UD58-B ) and an older HP 22" 1680x1050 monitor (HPw2207) with a VGA cord and a VGA-> DP converter.

My issues are as follow:

1) I can't get my vga screen with converter to use a resolution above 1280*1024

2) I'd like to use screen scaling because everything is so damn small on the 4k display. I'd want the scaling to only be done on the high-dpi display if possible.

Current setup:

I am using Nvidia drivers 418.56.

and normal higher resolutions are not available:

First issue: fixing resolution
I have tried to "addmode" using xrandr, but I get a BadMatch error. This is apparently normal with nvidia video cards.

My /etc/X11/xorg.conf file has been generated by nvidia usind sudo nvidia-xconfig :

The xorg.conf only contains one monitor, is this normal. I have tried to add a "Modeline" line under the Monitor0, but it didnt change anything.

Second issue : scaling

I have taken two steps to allow the HiDPI screen to display text and GUI in a more readable size:

1) System settings - fonts - Force Font DPI 144 (instead of 96)
2) system settings- display and monitors - scale display 1.5 (instead of 1).

I would lke these settings to only apply to the 4k monitor, is this possible at all?