Craiglist is quite good, I got a full darkroom for less than $50
BUT chemicals, is best to buy new
Normally used stuff is not bad, I'd be more worried about metal developing reels than plastic since those can be bent out of shpae.
If you buy either washing them thoroughly is a good idesa, plastic reels can be wahsed with baking soda and the mom-in-law toothbrush. With only a few drops of water to make a paste and then let it stand for a few minutes
As per chemicals it is always good to keep a sequence, fix before developer happens many-a-times
It is not a disaster... it is a character-building-experience
PS. depending on how many time you use your fixer it maybe safe to dump it down the drain. I prefer to use it less times so that there is little silver in there
Otherwise use jerry cans to collect your fixer, and put steel wool at the bottom. Then the Ag will stick to the iron and you can drain the liquid and take the sludge to a facility