3 gal is plenty big enough for your space. I would recommend looking into “mainlining” for a growing technique. With such small space to flower you definitely want them producing the biggest buds on the smallest plants possible.
also biggest thing is to relax!
I remember some of my first grows I flipped out on all kinds of stuff, thinking I had lock out, mites, you name the problem, and I’m sure I thought I had it. I’ve done so many now, that I do water only super soil with no ph check on water, no bottled nutes. All beneficial bugs, soaps, teas, drenches, no crazy pesticides.
biggest thing to realize....there are tons of ways to grow. None of them are the “right” way....it’s all about finding what works for you. Keep asking questions and paying attention to the plants as they grow.
One thing I will warn you about is that drip tray may be difficult to empty and keep clean as the plants get bigger. A solution I’ve used in the past, is to water each plant 8oz. Of water, every 15 minutes, until runoff is visible. This keeps you from watering too quickly and creating dry pockets in the soil. Watering slowly helps to evenly disperse the moisture throughout the soil. I also generally only need to water every 3 days. The plants need a sufficient “dry cycle” to grow their root mass quickly and strong. The dryness causes the plant to generate more root fibers to search for more water. Obviously you don’t want to take it too far and dry it out to the point of wilting, but the bag should be much lighter between watering. I hope that makes sense.