Quick question, what region of the US are you in, growing zone?
The 'money issues' thing is kinda BS if you are passing up locally sourced equivalents and paying big $$$ to ship *designer* amendments.
Pretty much, stuff like Oyster shell flour, fish meal (any type), crab/crustacean meal, etc., are only available "locally" in the PNW and close to the left coast. Great, if that's where you live, not so great if it has to be shipped.
Oyster shell flour is a prime example. The product itself is cheap, ~$9 - $12/40-50lb bag. To ship it is in the $40 neighborhood. Local to me is calcitic lime (a 1 to 1 equivalent), for ~$15 for the same amount. It's not rocket science to figure out the cost/benefit ratio between $49 and $15 for chemically equivalent products.
Bone meal here is right at $1/lb. Never priced the fish bone just knowing it would never be that cheap and I have yet to hear of any health issues arising from its use. You know, THAT would make the news. Nor from blood meal, but that seldom gets used now, being replaced with soy meal for a high N, slow release application.
Just saying, there is a literal shit ton of cheaper alternatives that bring exactly the same benefit to the table. Finding them just takes a bit of research and experience will show just how well they work, or don't.
I did the same thing you're doing till it became apparent I couldn't afford to keep doing it with shipping being so expensive. So, don't feel like the Lone Ranger here. LOL
The worst was rock dust. Paid $30 for 10lbs of basalt (IIRC), and then later found granite dust locally for $5/5gallon bucket. You supply the bucket and shovel. Weighed ~60-70lbs.
Now, pretty much the only bulk items that are worth the shipping are neem cake and kelp meal. Both are just north of $40 for shipping and both are worth the added expense IMO.
Worms: Feed as the food is consumed. Like GMM, I may only feed once/month in the winter and 2-3x that much when things warm up. If you can see food, they don't need any more. I do a 'lasagna' type deal with peat based bedding, adding ~1" of bedding when the food is consumed. Then, more food on top of the fresh bedding and repeat the whole thing. Ends up ~14"+ deep by harvest time. I do add some amendments to the bedding "just because", but don't keep adding them. I find worms from top to bottom giving lie to the 'they only stay near the surface' line. Your 4" depth seems a bit shallow, but experience will guide you in that area with YOUR set up.
HTH some.
Wet