How many cuttles are you planning on having? The bad thing about mysids is they are cannibalistic, so if you order 2000 you may only get to feed 1500 of them because the other 500 will get eaten by the survivors. Because this is the case, it may be a good idea to order 300-500 at a time so you lose less due to cannibalism. Then you would be ordering more times but in the long run it will likely save you money. You can give them some cyclop-eeze every couple of days for food. You can keep them in a very small space but make sure that the only water movement is by an airstone because they will get sucked up super easily by any intake.
As is the case with many animals, including cephalopods, with the food source is limited cannibalism will take control. As long as you can provide enough food for the mysid, you should not experience dramatic cannibalism.
Rather than using numbers, a number of people use volumes. Now this is a little different depending on what size container you hatch your Artemia from, but it is fairly close and can be modified if need be.
For a 10 gallon tank, I would feed about 10 ml of the artemia/water, twice daily. Keep in mind that the more feeding you do, the more water changes you may have to do because of uneaten food and the increases in nitrogenous waste products. You just have to play around with it for a bit to see what works best for your personal setup.
While 70,000 is fairly specific, we can't be sure if it is too much or too little because it depends on how many mysids you are going to keep together. For the majority of cases, 70,000 shrimp will be a large excess to what you will feasibly need. Also, cyclops or other very small food is a better choice than artemia.
I fed my mysids about every other day; a generous portion of cyclop-eeze. However, I seemed to only get to feed a very small portion of the amount I ordered to my cuttles. I would guess, on average, that I was able to get 200-300 mysids fed out of 500 ordered. I also did not have much luck with them shipping, and I believe that a large number of them died in transit, when they all did not die. So, I had live food for my cuttles 40-50% of the time that they were of the age that they would not accept frozen. I had 4 deaths, and I link every one of them to starvation.
I find a lot of loss with mysis from aquaculturestore.com. I believe these are wild caught, hence the low price and the non hardiness. Cultured mysids, like from reedmariculture.com seem much more hardy, and I experience almost zero loss when I use them.
Greg is right on about the cannibalism, and I feed them cycopeeze daily.