Ferrous sulfate is the common wetplate plate developer. Putting it in your ether would introduce it to the collodion before it had a chance to sensitize. I'm not sure what effect it might have on the silver bath. I would caution that it might adversely affect that costly solution.
Additional ether may not be needed anyways. You could try substituting 190 proof ethyl alcohol (and some use denatured alcohol) in place of any additional ether added to a collodion. I've had success with the ethanol method as have others who frequent the collodion forums. The denatured alcohols are toxic so I avoid them except to clean labware. There is some evidence that denaturing agents slow the degradation of working collodions and may actually reverse the aging effects.
Which collodion formula are you planning to mix?
If you must use ether, obtain the smallest amount you'll need and use it quickly. Quickly to me means less than three months under optimum storage conditions. Don't store any if you don't have to. Once opened, keep air out of the bottle to lessen peroxide formation. A gas blanket would work or you can displace air using glass marbles in the bottle as you use the ether. As others have said, keep it in a cool dark place away from ignition sources.
I don't know if
Artchemicals.com will sell to you without a business license, but they have the smallest quantitities (i.e., 50ml) of ether available that I've seen listed anywhere.
I have some safety links for ether and other chemicals used in the wetplate process in the resources section of my new online wetplate article (see sig below).
Joe