I have 1070 TI's so take this with a grain of salt but will do my best.
does it really matter that much? Are 1070 variants that different from one another in heat distribution, overclocking, etc?
I have a mix of Gigabyte, Asus and MSI 1070 TI's. They all perform very close to each other, about 500-510 sols/s each on equihash. I overclocked them the same. Heat distribution in my experience depends more of the design of the fans, my Gigabyte 2 fan cards run at 42 Celsius at 65% fan speed, while my single fan Asus Aero hits 59 degrees Celsius with the same fan speed. In the future I won't get single fan cards again, only dual fan because the cooling is definitely superior. Also, when 1 fan breaks the card will still continue to work because it has a backup fan whereas the single fan ones will overhead and stop.
Can I order another 8 1070s of any brand/model that is more available and I'll generally be happy, mining-wise?
In my experience, yes. I try to stick to 1 model (so only 1070 for example) but I've heard of many people mixing and matching models, even brands (AMD vs Nvidia) sometimes!
Is there any way to determine if I have Micron memory in Linux? Yes, I know about GPU-Z on Windows.
It really only matters for ETH I've heard so I wouldn't worry about it just yet.
Is there any way to upgrade the 1070 bios in Linux?
Don't think it's necessary for Nvidia cards, only AMD