I’m so glad I’m able to help!

Most chain pet store crickets don’t tend to live very long. Keeping them clean and well ventilated is key to all crickets. Their poop and it’s fumes kill them. I started with a plastic cricket keeper, but it lacks adequate ventilation. I now use plastic bins that I have cut areas out and hot glued in window screening where I want it, such as the lid and sides. Removing poop and uneaten food daily is essential. Honestly, try roaches. They are so much cleaner. For worms, as I already said, silkworms are great! Until you get him to lose some weight, try to stay away from superworms and wax worms as they are very fatty. Hornworms are good for hydrating treats...they are basically just bags of water. Bsfl (also called Phoenix worms, calci worms, etc) are also a great addition to staple feeders. They will eventually turn into flies, which are then fun little treats for your chameleon to hunt down. You may want to order from somewhere like Josh’s frogs or Linda’s gone buggy, so that you can order a variety of feeders in one shipment.
To manage Big Poppa’s weight, get a kitchen scale that measures in grams and see what he weighs. Start by feeding about 3 feeders, 3 times a week and see if that’s enough of a diet for him to lose some weight. You can weigh him weekly, but it may be a couple of weeks before you see any change. If his weight isn’t dropping, reduce his feedings by 1 insect until he does start losing some weight. Veiled’s are opportunistic eaters and always looking at you like you are starving them. Many nights my boy actually sleeps in his feeder and one of my girls sleeps right in front of hers. Speaking of feeders, there are things that will be little feeding stations in your enclosures. I really like these.
https://tkchameleons.com/products/shooting-gallery
Yes, the uvb is the long light that goes across the width of your enclosure. For a 2x2x4’ enclosure, you’ll need a 24” T5 fixture, just like the one in the link I gave you.
While not a necessity, these make hanging branches, vines and plants so very much easier.
https://dragonstrand.com/dragon-ledges/ They are well worth the price!
You don’t have to go bioactive in order to have live plants, only is you want a soil substrate on the floor. What makes it bioactive is that you have isopods and springtails which clean the poop and other detritus and keep things clean. For now, I’d suggest just keeping the floor bare.
Adding live plants will boost your humidity. If you are still having problems holding in humidity, you could wrap a shower curtain around a couple of sides or add the shrink to fit window insulation film. 30-50% humidity is actually quite drier than you’d think. I’m in humid Florida, but as I run my ac almost year round, humidity in my house is around 35% and much closer to 50% in the room where I keep my chameleons.
In terms of importance, getting the correct uvb and your supplement schedule are priority. Without these, your cham’s are at risk for metabolic bone disease (mbd) and some other possible health issues. Then changing your feedings will make a big positive difference. Next would be replacing the fake plants with live ones. A larger enclosure and the rest follows. It may seem overwhelming and so just keep in mind that it may take some time until you get everything where it needs to be. So many of us started where you are or with even less, but we got things corrected. I started 2 years ago with a young female veiled (didn’t even know she was a girl or a veiled), the equivalent of a chameleon kit with broken lights, a 1/2 cup of superworms and absolutely zero experience or knowledge of any reptiles. You can do this!