Ed,

One of your first contacts should be the Region II office of TWRA there in Nashville. TWRA has a publication concerning pond management that is a good start. They also have a program whereby a fisheries biologist will give assistance (in the form of advice) for pond owners. Also, the afore-mentioned sources of the NRCS and the UT Ag Extension folks will yield some pertinent info.

In your description, you have not indicated the size of the inflow from the spring, so I can not make a definitive guesstimate on the success of rainbow trout stocking other than to say if the spring flow is not pretty substantial, water temps may not remian low enough in the summer to sustain rainbows. Browns can tolerate a tad warmer water temps, but even then, I am thinking summer water temps in middle Tennessee may be too high for their survival. A potential additional problem may be low dissolved oxygen levels from the spring flow. I have found that most of the "true" groundwater I have tested had low DO. I would advise checking the DO content on this incoming water; you will want a minimum of 5 ppm. I have known of some pond owners who built their ponds with a spring inflow who had to aerate their ponds to maintain sufficient DO.

Next, I played with stocking smallmouth bass in the ponds of TVA's Land Between the Lakes in western KY and TN several years ago. (The US Forest Service has since taken over LBL.) I stocked smallmouth in combination with redear sunfish in some ponds; with fathead minnows and bluegills in other ponds. The smallmouth I stocked in all these ponds exhibited poor growth rates and almost non-existant reproduction.

Conversely, ponds stocked with largemouth bass (northern strain) and combinations of redear sunfish, bluegill, and fathead minnows resulted in good growth rates for the LMB and sunfish. The bass soon consumed essentially all of the fathead minnows. In my experience, if you stock minnows for a bass food source, you may have to conduct supplemental stockings of said minnows to ensure an adequate food supply. One thing you can do to increase spawning success of fathead minnows is to place mats of Spanish moss or loose straw bales in the shallowest part of the pond to provide the fatheads good spawning structure. (The Spanish moss is by far the best I have used!)

Therefore, based on my experiences playing with such things, I would recommend your friend stay with a largemouth bass/bluegill combination and, if he wishes to, throw redear sunfish into the mix as well. If desired, channel catfish can also be added to the mix, but they will need to be fed continuously through the growing season. The stocking rates I used were 500 young-of-year (YOY) bluegill per acre the first year, followed by 100 YOY largemouth bass per acre the second year. If I added redear to the mix, I would reduce the bluegill to 300 per acre and add 200 YOY redear per acre. If I desired channel catfish, I would add 50-100 fingerlings the second year. I haven't kept up with current recommended stocking rates, thus, a contact with TWRA would be most helpful for the most recent recommendations.

A couple of other observations I have for you that may or may not be of interest are as follows: A) DO NOT stock crappie in the pond. Yes, I know some folks do so and have a decent crappie fishery in some situations. These are the exception rather than the rule. However, in my experiences, most of the time when crappie are stocked in small ponds, you end up with a very stunted population about 5-10 years down the road. If you do stock crappie, harvest them with a vengeance. They are highly prolific (again, in most situations) and will soon overpopulate most small ponds.
B) DO NOT stock pure Florida strain largemouth in ponds in Tennessee. Research I have seen shows the Floridas will not grow as well as the northern strain at our latitude. I have seen some data on Florida/northern crosses that show increased growth rates. However, the expense of these hybrids may not justify the end product. Additionally, there is some question about successive generations of bass that result from reproduction of these hybrids in terms of growth and survival.
C) Harvest the fish from a pond in a sensible manner. DO NOT overharvest your predators (bass) or stunting of the bluegill will result. DO NOT overharvest your bluegill or the bass will run shy of food. Check the "balance" of your pond via seine hauls to determine size structure and relative population of your bluegill and YOY bass. Dr. Swingle of Auburn University developed the Southern standards for pond balance many, many years ago. For the most part, those standards are still relevant. Again, the TWRA pond management book and/or the TWRA fisheries biologist can assist you with advice for this effort.

I hope these points help!