Ok, I'll show you whats wrong and right step by step here.
"1. i am feeding my pacman goldfish,pinkies and crickets.i feed him a pinky,he is fine for a week, then i switch to goldfish that week and crickets the next and etc, is this a good diest for him? "
Ok, no rodents shoudl be in it's diet at all because they cause blindness, and I'm looking into goldfish still but they should only be offered occasionally.
What size is your frog? If it is still small it should be eating a meal of about 3 crickets every two days of so.
"2. i was wondering if sand would be a good sunstrate to use in his water dish,so he could burrow in it, sice he spends 95% of his time in it? "
No, I wouldn't use sand for anything with these frogs because it may cause an impaction. And it doesn't matter if it's just in the water dish since sand sticks to everything. He shouldn't need anything as a substrate in his water dish.
Try something like bed-a-beast or eco-earth for a substrate for the land section and just the water dish for water. And do not use undertank heating, use a heat lamp.
"3. i want to get another pacman and was wondering if i bought a ten gallon tank and put one of those plastic dividers in it would that work? i mean would it stress the frogs out, if they saw eachother and etc? "
No, do not put them together in the same enclosure regardless if it's siliconed off or not. The chances of spreading diseas is even greater than the tremendous amount of stress this will cause on both frogs. I suggest a separate 10 gallon for each frog.
Oh, in case you are wondering what my qualifications are for this information I own 5 cranwells' horned frogs and 2 surinam/amazonian horned frogs, and have been keeping this kind of frog for 8 years now.

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