Nice project BM. The pond liner isn't real cheap,neither are the pumps,but with a little bit of research and scrounging around for parts you should be able to build a bio-filter.Check out some of the Koi sites for tips on ponds.When you get ready for plants in the pond let me know and I will get you a red water lily(got one in my pond) and possibly some other plant starts.
When I was in the landscape construction buisness I built alot of ponds and it is very costly for liner and pumps, but like mentioned above you can probably make your own filters and what not, remember the bigger the pond the bigger the pump and liner(do not use plastic) trust me, and as for depth it depends on what kind of bass and how many you plan on having in your pond, most of the ponds I built had small water falls in them that will also help with oxygen levels in your pond, good luck with your project its alot of work and maintinence.
I've built a couple of ponds and waterfalls. Its not cheap for the liners, pumps, wiring, etc... I'd also recommend putting motion sensors on a couple of sprinklers to protect your fish from *****, and herons. I've lost a ton of fish without them. I made my first pond back in Junior High for a project. Its a lot of fun, I think.
We recently finished building our new house on 5 acres. It was raw land and we left most of it natural, except where we needed to clean up our view. I have to build another Koi pond in the backyard, and A larger pond that I will plant with trout, bluegill, or both. The small pond is already dug, I'm just waiting for the weather to get a little nicer before I finish it. The bigger pond is currently under water. Probably 1/4 to 1/2 acre. It seems to gather and hold quite a bit and it stays about 9 months of the year. It has a small culvert that runs the excess off a hill. If I stop the culvert from draining, it would hold water all year. This August when I get back from salmon fishing in Canada, I'm going to rent an excavator and clean it up, and shape the pond. I suspect that I will hit a spring as there's really no reason for water to be there in the first place. I'll let it fill up over the first rains of the fall, and hopefully by this time next year, I'll test the water and be getting ready for fish!
There are several books on building ponds available. I even saw a couple at Home Depot. Good luck, and keep a picture record!
i have made 2. the first was when i was about 11 or 12 and i dug about a 6x 4x1.5 pond in the back woods and put catfish in it. the biggest mistake was that i used dirt as the bottom so it was always murky then the J.O. landowner filled it in for "liability" reasons even though there has never been a building within a 1/2 mile from it.
the second was when i was in hight school, i bought a 12' round by 3' deep swimming pool, used pea gravel, rocks and small boulders for the bottom bought a few pond plant from the nursery and got a few froma nearby pond and a few sticks. first i put 2 channel cats of about 15" in there. to feed them i put in exactly 51 feeder fish from the pet store. after a couple weeks the cats hadn't eaten any. then i put a 4-5" LMB in there. The next day i went to see and he had eaten every single feeder, no lie. I ended up putting a few more small LMB in there and it was alot of fun to throw hoppers and crawlers in therer and all kinds of stuff for the cats. eventually i had to release them back where they came from, a slimy runoff pond that nearly dries up in the summer. didnt need a pump for these type of fish as long as it has access to rain and you keep a little flow in the summer.