1) I believe most IR rangers actually have a mininum distance, that if you go below, will cause there to "appear like" there are objects further away. If you hook it up and have it print the distance reading, it's easy to see.
2) You don't actually supply precisely 700mA; you just need to make sure that the voltage input is within the specified range, and that your power source is capable of supplying AT LEAST 700mA. Most batteries should be capable of supplying 700mA. It's easy to test, run one sensor at at time, and if you connect two and it doesn't work for some reason, try adding more batteries in parallel. If you are using a wall AC adapter, just make sure that the rating on it is > 700mA + your other power needs.