#2. Yes, you can use the plastic. Light for summer -- dark for winter. Tape it or use a bungee cord around the eBucket. Main reason for any cover is to keep the backsplash off your plant. Less chance of disease.
#3. Tomatoes -- not less than 5 gallons, preferably 10 gallons or larger
cukes, zukes, winter squash(s), peppers, eggplant, and broccoli will do fine in a 5 gallon eBucket.
Eggplants, broccoli, cabbages, cauliflowers all require 1 plant per 5-gallon eBucket). These plants like organic mediums so you can supplement your potting mix with aged compost, decomp leaves and it will go further.
#4. Bocabob's automatic drip system will accommodate 45 different drip sites on one sytem. Instructions are attached.