Stem on plant appears to be narrow at the bottom growing beefier up higher

It seems to be genetic or that there wasn't enough light during the early seedling phase. Either way, it looks like you have room in your pot to add more soil. You can bury the lower part of the stem and roots will grow from it. I would do it just in case the plant tips over because it can break, being that it is a weak spot. I also noticed you are feeding the full dose of fox farm nutes. I know the feeding chart says to use that but it is an easy way to nute burn your plants. I start off with 1/4 dose then go up to half dose the next feeding. Since you started the plants in a large pot, the roots haven't colonized that large space so nutrients and water are collecting in the soil not being used. You can see discoloration and leaf tip necrosis already.