My two cents after two grows in a 4x4. LED lighting & strength? It's just so frustrating trying to figure out how high to hang your LEDs to guesstimate the PAR values. My
HLG 600 has a dimmer control as well, so really it just becomes impossible to know how to set the lighting, unless you measure it. I finally bit the bullet and bought a good PAR meter, and now the process is as simple as can be. I raise or lower the light to have some working space, and I adjust the dimmer to get the light strength I need. Takes two seconds, and I know what I have.
Second, a tip on fabric pots if you do LST training. Get a simple handheld paper hole punch and it will put a nice round hole where you want it. I put holes every two inches around the top of my pots and had lots of places to attach plant ties.
A tip on pH - don't believe a cheap meter. I had a $12 handheld pen I used last year, and it read quite high in retrospect. I bought a
Bluelab controller, and then a ($75) Bluelap pH pen, and calibrated them. Both of them match, and both read about 1 point lower than the old pen.
Heat/fans - I have a temperature controller that turns on when the tent hits 80F and off when it gets down to 77F. I have a 6-inch fan that can change the air in the 4x4 every 60 seconds. (Makes it impossible to control humidity though.) I have a humdifier in the tent as well. In the last 24 hours my RH has ranged from 28% to 78%, with the high point coming at night when the fan shuts off. I have the tent in a bedroom with the door closed to keep the humidity up in that room.
In my first grow, a year ago, I didn't have a) a strong enough light, b) a good pH meter, and c) a good PAR meter. I started with a $500 kit consisting of a the tent, a 120W LED light, the fan, and some controllers. After getting about to the flowering stage with first crop I bought a $700 light. And after getting frustrated by burning my plants I got a $400 PAR meter.
Second crop went much better after some experience and having actual measurements to work from. I found how frustrating it was to try to trim and clean around 5 plants in the tent so went to only 4 for the next grow.
Partly as a result of the crowding in the tent making it hard to water, trim and clean up the two plants in the back of the tent, I went with a DIY irrigation system as described by cocoforcannabis.com. It works well, but this grow has been all about understanding the water conditions and controlling them. I have to understand it better now because I'm growing in Coco. That led to one more largish expense, a $400
Bluelab pH controller, which I use to keep control of the water reservoir. I have a timer on the irrigation pump, and I have a sump pump to remove the old water and dump it into a bucket. Now I'm getting deep into understanding silicone, and cal/mag, and EC-measured-runoff and the like. Plants (3 weeks old) are looking pretty good this time.
Of all the stuff I bought, nothing seems to make more of a difference in terms of control than the PAR meter. It really helps.