seashores,
I'll offer some comments from a DIY pond builder...I'm not a pro, but a DIY pond builder. See last paragraph, where I recommend you NOT do the first pond yourself...only attempt after you know full well what you are getting into...this isn't at all like an ornamental pond. It is hard and dangerous work, not to be taken lightly.
1) First, make sure you understand what you are getting into...by my rough calculations you are looking at a minimum of 42000 cubic ft of dirt in the dam of your first pond. That's a lot of dirt. Estimate how much dirt you can move in a pass with the loader and calculate more accurately the amount of dirt required and measure the time for each pass...you can then get a rough estimate of the total time required.
2) You may very well run into rock and/or very hard clay to cut...will the loader do that job?
3) I doubt that the loader will pack the clay sufficiently to insure against leaks. Dozers can do that, but even then you must go very slowly, i.e. build up a few inches and pack before building again. It is very time consuming and if you are not prepared for that, then you might want to re-think. Also, make very sure you have adequate moisture in the clay to pack it...its very dry in Texas right now and not a good time to pack clay.
4) Go to the USDA site and download publication 590. Read it. It will tell you precisely how to plan out the dam and calculate the amount of dirt to be moved.
5) I don't know the capabilities of your loader, but doubt very seriously its ability to dig the core trench.
6) Always think safety. Operating equipment especially in a pond building situation is dangerous, even more so for the beginner. That inside slope may sound very harmless but it will look entirely different from your loader. It is easy to seriously hurt yourself, even kill yourself. I'm not trying to scare you, but there is a reason for professional pond builders...if it were easy, there wouldn't be the pros.
In summary, my advice to you is do your homework. Hire the first pond to be done by a professional. Watch carefully, even help with the construction, then and only then attempt to do it on your own...and make sure you have adequate equipment for the job, before ever turning the first dirt.