should I tweak values in framebuffer when I am going for vfb+
You write this confusingly but I guess by framebuffer you mean 'Corona framebuffer'. Because VFB+ is also framebuffer, just native 3dsMax one.
It's one or the other. If you plan to use VFB+, you select native framebuffer, you keep all color correction in Corona in linear format (1.0 HL, 1.0 Contrast) and also keep default 6500K White balance. Exposure is arbitrary so it doesn't matter but it should always be set roughly correctly or slightly underexposed for correct MSI behavior.
Then you can use color correction in VFB+.
I read a lot about keeping it linear - HC 1 and contrast at 1 when exporting an image to 32bit exr
Only if you need linear output for compositing or exposure tweaking. You can export .exr with Highlight compression and contrast, it will just be clamped. So the choice is purely dependant on your post-production workflow.
Is there any correct approach to highlight compression and contrast in framebuffer or is it all just artistic way of choosing the right values ?
It's kind of both... The default highlight compression in Corona, which is Reinhard, is not that good looking without further post-production (local highlights recovery, saturation, contrast) , not sure why it's so universally popular.
The filmic in VFB+ does better job, specially in keeping nicely saturated highlights.
But outside of that, it's scene dependant creative choice. You keep it as low as possible to avoid burn-outs without sacrificing too much which would result in flat and dull look.
Now burnouts are my specialty, I can't even count how many people asked me over the years "Help, my interior is either dark, or blown out/burned around windows !!". Well.... you either light it in way you need as little tone-mapping as possible (if that means flashlights/softboxes like photographer would do), or you bring it down with tonemapping, in exchange for flat look. There is no "holy grail" solution to this problem, no secret settings to lighting and photorealism.
