what's a good brand?

It varies by country/region.  The best way to do it is to look to your local health food and/or whole food stores.  Always go for food grade since that will be the purest and least processed.

and what's the best way to store it to prevent solidifying or separating?

If you have a wine fridge, then put it in the bit for red wine.  Don't put it in the bit for white wine as that's too cold for your bits.

If not, then keep it in a cool place out of the sun.    My laundry room/pantry is the only room in the house that doesn't have underfloor heating so that's where we keep stuff like that.  The kitchen is too warm.

coconut oil is said to be good/alright for jerking off
does anyone use it? yay or nay? what's a good brand?
and what's the best way to store it to prevent solidifying or separating?

I've tried coconut oil (bought from Starwest-Botanicals) but didn't really like it (it was too oily for me). I did a little online searching and found Sliquid; it is pretty good. I bought, and tried; Natural, Natural Gel, and Oceanics. It's pretty slick, and easy to clean up. I personally recommend it