All marble etches, and stains, and chips, and has stun marks, and scratches.

If you can live with patina happening to your marble, then you should use it!

My concern is mixing the white marble with a white quartz ...

"I’m up to the task of spray sealing it monthly/every few months"

Please note that sealing will help with stains, but will not prevent etching. Also note that a polished finish (as in your OP photo) shows etching more glaringly than a honed/matte finish will.

Many people love marble and are fine with its etching; it is just the nature of marble. But it does bother others, so this is a personal choice, and make sure which kind of person you are. If you decide you are OK with etching, I recommend you find a marble for your island that has a honed finish, not the polished finish in your OP. Also note that your willingness to seal monthly may not be a good thing as that much sealant may cause your stone to have a haze. I'd recommend sealing marble 3x a year to prevent stains.

I am not sure if you know what "etching" actually looks like on marble.

It is a slight dullness in the shine which generally can only be seen when the light hits it right and one really looks for it. My friend has had marble counters in her kitchen for many years and her family are not careful with it. When I was starting my remodel I asked her about etching and I had to squint and look carefully for any of the small areas where it had etched. In normal use I had never seen it.

In other words it is not some horrible "scar" in the marble. Many bistros and bars have marble counters and they are etched only it is called "patina" which has a nicer sound.

You don't need to seal it that often - once a year is more than sufficient.

I have both honed and polished marble in my bathrooms. The difference is that the honed finish has a satin soft sheen to it and the polished is very shiny and reflective

ETA - Interesting that your marble appears to be cool tone. I selected a marble that also lacks the iconic strong marbling for my master bath counter but mine is French Vanilla which is a warm tone with no "gray". Even among the slabs in the same lot there was a lot of differentiation but luckiiy I was able to snag the one that I liked the best.

Im considering white rhino marble and dont mind etching (i dont think), but i would mind a stained red ring, for example. does sealer prevent discoloring?

I have a honed island. Only regret is builder did a light ’seal’ before install, which means no seal protection at time of move into house (new construction). Etch ring and stain on day one. Made mistake of using baking soda to remove stain and etched surface. Plan now is to live with scuffs, seal twice yearly (DryTreat two coats), and resurface island

($1K) before home resale.

"All marble etches, and stains..."

No longer; technology has solved those problems.