Hey Daveacr first things first great job, especially for the first time. Looking nice and healthy only seeing one leaf with a minor deficiency second pic front row the girl on the left(looks like magnesium but would need a closer picture to be sure). If you have the space in your new tent setup you could raise the stronger mars LED higher till temps are fine. 28C is ok for first 3-4 weeks of flower but keep in mind temperature is only a part of your environment, humidity is just as important. You want to steer your plants transpiration, high temperatures need higher humidity levels, here you can stick to VPD charts to find perfect conditions(google vpd chart LED grow). If raising the light isn’t enough you might want a bigger exhaust fan to keep everything in a good range. If you live in the northern hemisphere winter is your best friend, temperatures become easier to control and indoor radiator air is nice and dry.
With the color changing of the leds you can steer the stretch a bit, warm light does make them stretch more colder spectrum does let them grow a bit more compact, but you can definitely go from seed to harvest with just one setting or even mix both, no worrys.
When it comes to watering, i always liked to feel the weight of the pots to know if irrigation is needed.
Thickness of stalk and branches are mostly determined by genetics, airflow does also play a part here so a fan that blows air around (not onto the plants) is a good investment.
There are also fancy additives like silica that are beneficial for stronger stalks and branches btw but not necessary, commercial grows also go mostly without them.
I did also go without PH meter my first grows on soil, but need to say they turn out to be handy when you run into issues with deficiencies and lockouts, always good to measure what goes in and what goes out when things go wrong. There are cheap ones on eBay for like 10 bucks that work but you might want to spend a bit more and get one that you can calibrate, its quite some waste to buy every few month a new one to be sure the numbers are right. But in the end looking at your pictures you seem to be doing alright without one for now