I have 16m upkeep and 700mp/hour. Am I making upkeep very well? If it helps, I'm rank 81.

16m upkeep is very low. You might want to research better mods and start installing them. As for now... your mining should be sufficient enough to handle your upkeep for quite a while.

How much upkeep could I support with 700mp/hour? I could install 5 deep core neutroniums right now and raise my upkeep by 20m.

Collect an hour's worth of shipment and sell the minerals you get in that shipment, keeping track of how much you earn. Multiply it by 24 to get an idea for how much you can afford.

You'll want to save enough after upkeep is deducted so that you'll have enough for planetary upgrades, unless you're also selling stuff to supplement your income (in which case mining doesn't -really- matter).

If you want a comparison, I'm a rank 86 with a 35.4 million credit upkeep. My minerals are lower than yours, at 674 per hour, but I'm living quite comfortably (however - the majority of my income is from selling artifacts, so it's a little different...)