When you decide what type of plant to grow, you will want to plant the appropriate number of seedlings. The bucket can accommodate 2-3 plants per bucket. I have planted up to four tomato plants in one bucket! they all tend to do well as clustering like this actually bunches up the foliage and tends to protect the plant from overheating.
If we were growing bell peppers as an example, you could comfortably plant three in a bucket. How you arrange them is important. You will want to arrange them opposite to where you will lay your fertilizer.
I will be planting two Hot Pepper seedlings that I picked up from the nursery today... They have already started growing gigantic fruit - they are called 'Cowhorns' peppers.
Now you will need to cut an access into the lid to allow you to insert the roots and stem into the access hole then plant the seedling in the top of potting mix. If you have 3 seedlings then you either cut three separate holes along one side of the bucket or one long hole to accommodate the seedlings. I have come to prefer the single strip as shown below...