Butzy, sorry I haven't responded but work has been a real bear the last few days and I haven't really gotten on here much. To answer a few of your questions:
-I have used food grade plastic buckets and they do fine although if you start to really get into fermentation I suggest investing in a crock or 2. It doesn't have to be a fermentation crock, just any crock will do as long as you know that lead was not used in the making of it (many old, vintage crocks did have lead in them and if the glaze is chipped or cracked it can leach into the foods).
-If I am making a brine (which is usually unless I'm making sauerkraut) I use a ratio of 3 tablespoons + 1 teaspoon of salt (kosher or pickling-not table salt) for every 8 cups of water.
-Your temperatures seem a little high for proper fermentation but give it a try, just start checking things earlier than what has previously been suggested as fermentation will start more quickly and proceed more rapidly.
-What to look out for:
-surface mold- check your ferment at least once a week, if using the set you are suggesting. Chances are you will get some surface mold. Just gently skim an of this mold from the top of the brine, wipe down the bag you are using as a weight and wipe down the sides of the fermentation vessel. This is a common occurrence and does not necessarily mean anything as gone wrong
-if your product or brine starts to take on a red tinge (red radishes, red cabbage, beets will turn the brine red naturally so this is not what I am talking about) then you will need to throw it out. You got some nasties in that brine and they can make you sick
-while there is a certain "funky" smell associated with fermenting foods if you get a moldy or smell of mildew in your product taste it, if that smell translates into flavor then you probably need to toss, but be careful here, to those uninitiated in the flavors of fermentation your first bite of a truly fermented food can seem like it is not right. That's because you are expecting it to taste like a normal pickle and fermented foods don't taste quite the same. They are a little more complex with just a hint of "funk" to them
-if your veggies turn soft or mushy something went wrong (and this may be an issue you experience with your higher temperatures). Fermented veggies may not always be crisp or have a snap to them but they definitely shouldn't be soft or mushy.
Hope this answers a few of your questions.