First, I am not going to tone in my darkroom. That'll be done outside as I have no ventilation capability in my Dr.
That said....
I saw conflicting information so I'll have to ask. What is the risk of storing concentrated and working solution in the darkroom - to me and to my supplies such as some paper and some film? I know some toner can fog these supplies. While I store bulk of supplies outside my DR, amount used for fairly immediate use are stored in dr. The "solutions" will be stored in a plastic bottle with a tight fitting cap. Is it the best to keep it elsewhere or would it be as "ok" as having fixers and developers?
Selenium toner is not one of the fume / fogging toners as far as I know. The sulfide toners are the bad guys on that one. If it is a toner and it stinks like well rotted eggs, it is one of the toners who's fumes will fog paper. Selenium has a different odor. More ammonia smell. Your nose might not like it, but your sensitized materials should be fine.
I store my liquid chemicals in low sided plastic tubs. Still easy to get to but would contain the liquid from a failed container. A little belt and suspenders just might save a cleanup issue in the future.
Yes, I do that too. I keep all of my liquid concentrates and stock/working solutions in deep plastic tubs with lid. On my processing table (wet side), I have a giant shallow plastic tub and trays are inside it. As my DR is a converted spare bedroom, it is carpetted. I really don't want to spill anything or I'll have to rip up the carpet.