Questions about fish and rocks

I'm no expert on this, but I really think you need to go with a deeper pond.
Hopefully some others will offer more advice.

a pond where the fish are going to stay in over winter it will have to be at least 2ft deep.

if your inteading to keep koi, has to be over 4ft for the growth of the fish.

as for rocks, poor a little vinegar over them if it fizzs then don't use them. if nothing happens they should be fine. also check if there is signs of metals ores, these rocks should also be left.

if your make it 2ft then it's fine for goldfish, it's about 350 gallons (uk) and can be home to around 7 goldfish (10max). don't introduce all of them at once. this pond will have to be filtered as goldfish are waste producing machines.

types goldfish - comets, commons, shubumkins. fancys will have to be taken indoors during winter.

on the sides it depends on the type of soil you have. if it's a loose sandy soil it'd best to have them sloped. it's only a problem when the pond it empty, when full the water should hold the sides. you could make the sides stronger with ply wood if you want striaght sides

make sure you protect liner with carpet, newspaper etc.

the planting edge bepends on what plants you want. you can get lillys that will be fine in the 30 inches parts. best thing to do is check out the plants in the store pick which you want then dig the shelf to fit them.
or dig the shelf about 12inches deep by around 12inches wide then you can always higher the pots up with house bricks.

safety, kids, and dogs

Straight sides will be better for the fish as it prevents predators from standing on a ledge and fishing for lunch. Sloped sides are dangerous for dogs and kids who might fall in and not be able to get out, shelves or ledges allow them to climb out, liners are terribly slippery with a layer of algae. Ledges make it easier to set plants in at various levels, but make it harder to catch sick fish that require treatment.

Do consider how you can catch a fish, perhaps keep ledges and such on one side, so you could lower the water level to contain the fish for easier capture. Otherwise you can set plants on plastic cartons and such, and remove if necessary, but they may be less stable in wind than plants on ledges.

Also, you really, really want to install a bottom drain during construction. You will be very happy if you do this now. It is important to the health of the pond that the bottom be kept clean of solid wastes.

And, be sure that you have a GFI protected electrical outlet and easy access to water. You will have a lot of evaporation, so you will be refilling the pond a lot, and yet you will still have to drain and remove some water to keep the water parameters correct. Fountains and waterfalls will dramatically increase evaporation so don't plan to run these all the time, have some filtration running that does not go through the fountain if you have one.

There is a Gardenweb forum for ponds that is great.

I have a pond that went from 240 gallons to 2000 gallons, I got sick and tired of feeding the local raccoons and herons, so when it was dug out I made the sides straight down and 3 1/2 feet deep. I have no children so that's not a problem for me. Now my fish are happy and I don't have to worry about anything bothering them. In my pond there are koi, goldfish, turtles,frogs and mosquito fish.