I will provide a little advice on a couple of your questions. I don't like tackleing multiple questions because it ends up taking lots of my time due to complex answers to what seems are simple questions.
Firstly, for benefit of all readers - I will assume that REB means redear sunfish (RES).
My advice is not rosey but hopefully it will help you understand what is happening in your new pond.
1. It's too late now, but according to the Pond Boss philosophy, your stocking plan is somewhat biased. Two reasons, 1. you have added all the species at once. Typically the predators are added later after minnows and forage fish have spawned AT LEAST one time. This produces lots and lots and lots of small forage fish for fast growth of predators when they are stocked later. Small fish fry can also enhance growth of panfish. Medium and large panfish will feed on fish smaller than 1".

2. You have added a full complement of fish (all species) before the pond is completely full. Basic rule - A full pond overall, produces the most and best food item diversity for a "FULL" commmunity or combination of fishes. When the pond is not completely full, stocking of just forage fish (primarily minnows sometimes panfish) is the best plan for the first or initial stocking. If one is truly interested in good growth of their fish, stocking should be done in 2 or 3 phases over a period of 1-2 yrs. Phase 1: minnows and maybe panfish, Phase 2: predators, and maybe extra or new panfish, Phase 3: some supplimental stocking to correct or adjust densities to improve the fishery balance.

3. Lets look briefly at your stocking work so far. Reminder - you have or will have 3 acres of water. You stocked 40 lbs of minnows(FH) and 200 LMB 4"-6". Bass this size no longer eat zooplankton. Your unfilled pond does not have a full complement of invertebrates compared to full pool - so invertebrates are less than adequate for the bass AND have to be shared with the CC, CBG, and RES. Minnows of 40 lb X 16 oz = 640 oz of FH. 640/200LMB = 3.2 oz per bass - not much food that will not last very long. Now bass are on a low food diet. I like to see at least one pound of existing forage fish for each 4"-10" bass (or predator).

4. In a filling pond, it can be hard for some fish to produce adequate spawns due to fluxuating or rising water levels. Filling ponds are frequently muddy or silty-turbid which can stress egg development and hatching success. Rising water levels can also affect proper nest construction or desire to nest by males of the sunfish fish family. This is another reason to wait to stock the sport fishes until the pond is at full pool.
Panfish should be spawning in TX by now, but since your pond is not at full pool your spawns maybe delayed for several or a combination of reasons.

5. If your water is cloudy-muddy you may not see the minnow fry. This assumes you still have minnows and each bass has not eaten its 3.2 oz share of FH. Realize some bass may have eaten more than their 3.2 oz portion by now. I estimate that a 6" bass will eat 3.2oz of minnows within 2 wks. EXPERIMENTING POND MEISERS MAY WANT TO ACTUALLY TEST THIS. IT WOULD BE AN EXCELLENT LITTLE 1/2 TO ONE PAGE ARTICLE FOR PB Mag!! Put a 5"-6" LMB in a aquarium with 3.2 oz of fatheads; measure how long the minnows last.

6. Tilapia will almost always winterfill due to low temperatures in your area. Tilapia can grow larger than bgill and in my opinion they are as good as or better eating than bgill. Meat has a texture and flavor similar to crappie and a better texture than CC.

7. ""Is five hundred (300 CNBG, 200 REB, 40 lbs of fatheads) enough for a three acre pool""? Larger sized CNBG and RES are acceptable but not best. FH stocked numbers are okay with out bass present; with 4"-6" bass and your pond conditions FH should have been at 200 lbs(100-300) in my opinion. It would have been much easier and MUCH more successful to have stocked your 200 LMB this fall. Ten pounds of FH minnows stocked in spring without bass would have easily produced 100-200 lbs of minnows by fall.

8. I am on a roll, I might as well finish your questions.
""Why am I not seeing brim and catfish feeding at the feeders?"
It all depends.
If your new pond has water clarity issues with newly stocked fish don't expect immediate responses at fish feeders. Firstly fish have to find the feeders. Often fish have to be CONDITIONED to eat artificial food. Secondly, sometimes even hatchery pellet trained fish will go off feed or will refuse to eat pellets when placed in a NEW environment. Thirdly, your feeding schedule may be different than what they were used to. AND your fish may not have been raised on pellets. Fourthly, it is very possible they do not know what fish food is yet or they have not located the feeder/s. Fiftly your pellets can be a different brand, flavor or protein content than what they are used to - some fish are picky just like people. Numerous reasons are possible, obviously it is some reason or combination of reasons. BE assured numerous people have this same problem of new fish not eating the pelleted offerigs. Very frequently, it is not just a matter of tossing out fish food and the fish go wild for it.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management