QD - you are on the right track. You will be really glad you happened onto PB when you did. If you have not done so subscribe to PB mag and consider some of the other products (books etc) to assist you in reaching your goals.

Your goals are very similar to mine, except I want a larger predator. I am going for BG-YP-SMB-HSB. I am concerned my pond at 8' deep will prove to be warmer than the SMB would prefer. THe HSB will be to control the BG.

Going deeper is a great thing to do for several reasons - more water = more fish carrying capacity. More depth = cooler water at deeper levels, plus more water (total volume) heats up and cools down more slowly - reacts less to changes in air temps (good for the fish and other creatures that live in the water). More depth will allow you more species choices and places to put structure to enhance fish developement. There a ton of threads on here about structure - try a search and see what else you can find.

Re your geo unit outflow -here is the math: if you have one acre (43,560 sf) at an average depth of 5' (you are now going deeper) that is 217,800 cf. Each cu. ft = 7.48 gallons so you would have like 1.6 million gallons. Adding 11 gpm of 60 degree water will not change the pond water temperature that you will be able to measure. You can if you want go through measuring the heat content of the two waters but trust me it won't affect the temperature. It is a great idea to add the 11 gpm assuming especially if the water is coming from a well or other source away from the pond.

Given that you seem to be diging in undisturbed topsoil, you should get the soil tested for clay content. Your local county extension service will probably have a guy/gal who will come out for free and do some sampling with a boring device. If you don't have enough clay and build your pond from loam type soil it will leak. Meaning you may have to import clay to put into the inside of the pond after digging to seal it against leaks. If you do not know what you have this is probably the most critical step so far. A leaker is a very expensive headache once the water is in it and the excavating equipment is gone.

I would suggest purusing the threads on "Pond Construction" - including "selecting a site" and "soil questions".

Keep asking - you will get the help you need here.

2/3 acre pond 12 miles from that big pond we call Lake Erie.