There are several resources on this site:

Ensuring Art’s Longevity: Strategies for Durable Oil Paintings

https://10cd20aa9b.nxcli.io/excessively-thinning-oil-paint/

https://10cd20aa9b.nxcli.io/oil-painting-practices/

https://10cd20aa9b.nxcli.io/yellowing-of-oil-paint/

I also recommend the Painting Best Practices course. It is comprehensive…

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From your text I read that the yellowing happens in spots? In that case maybe it is more due to something else than the oil? Darkening/yellowing from darkness will generally affect the whole surface, but be more noticeable in the light areas.
Driers and resins yellows at a faster rate than oils, and is as far as I know permanent, but I am no expert.

Hi Luca
I think I can answer a few of these.

1. Yes, nothing wrong with oil priming over acrylic gesso. It would be very similar to applying oil paint over acryllic gesso. Also check the manufacturer’s guidelines.

2. I clean my brushes in oil (no clove), then soap and water. I would not add clove oil, since that would need to cleaned out of the…

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If you glue primed canvas or linen or another support to your panels, you typically don’t need to size.

Under a lead oil ground you should definitely apply a coating to prevent oil from the ground and paint to penetrate the wood. I believe one coat of Rublev Fluid Medium is sufficient (for oil, two for acrylic).

You asked if people have mixed and measured. A few have done both. Graydon is one of them.

Personally, I mix and tube my own N3 and N7 in addition to the N5 from MH. I typically use chremnitz white, ivory black and raw umber or raw sienna to mix. I measure against a Munsell grayscale. It is accurate enough for me.

I mix my own Regalrez, that has been really easy to do. With proper drying time and cleaning before varnishing, the results have been very good. Also, lead oil grounds have improved my results over the acrylic primers/gessoes.

Finding a solvent for the Laropal has been more cumbersome..

Michael Harding makes an N5, but it used to have zinc white in it. That could have changed since I last checked. Apart from that you could reach out to Graydon Parrish, who does a lot of color experiments, including measurements.