Since ESV is supplied in a "just fill it to the line" package, they're still good to go. The concern with storing calcium chloride that you have to weigh out is that it's hygroscopic and can absorb moisture, making the weight a bit "off" when you use it.
A few posts ago you mentioned that your pump is "kalk safe". As others have mentioned, that's not actually the concern. The concern is that your pump and/or pickup tube gets into the undissolved kalk on the bottom of the container, and that gets pumped into the tank, wiping out everything.
With respect to dosing pumps, you generally only need 2 channels, which is why the Apex D.O.S. system has only two. However, some folks want the "extra" pumps in a 3, 4 or even 7 channel dosing pump to do other things. The GHL system, for example, uses a couple of channels to run automatic alkalinity tests.