Pot size

[solid7]

Hoping to plant in 4 1/4 gal. food-grade white buckets. Where should the holes be drilled, how many holes, and how large should the holes be?

 
A single half inch hole is sufficient to drain a bucket.  More holes won't increase drainage, but it may provide you piece of mind that you have some redundancy, in case your drain hole gets plugged. (sometimes ants like to dam them up)

 

[Swartmamba]

Certain varieties require larger pots. Season length makes a difference too. I use 3 gallon fabric pots for most year 1 plants as my grow season is short. Year 2 i go to 7 gallon and year 3 and up 15-25 gallons. If your summers are extremely hot then a larger pot is far easier as you dont have to water it as frequently.

If you are planning a organic grow i would recommend a 7 gallon pot if you are going to feed with every watering you can get away with a smaller pot