There have been tests of the stopping power of ice.
Only high power bullets can get through more than 3 feet of solid ice at freezing temperature. If ice is significantly colder than freezing, it is much stronger. Since ice is rarely used as a building material, data on this is relatively scare, but I seem to recall ice was about 5 times are strong at minus forty than it was at freezing.
Frozone seems to use ice that is closer to minus 40 than freezing, so I would assume 1 foot of his ice would stop most bullets.
I watched the scene with Frozone in the jewelry store multiple times. Frozone freezes the officer first then the gun is fired - presumably when the officer realizes he has been attacked, but before the freeze attack is complete. Flow rates are not really applicable in the sense that water is not flowing from Frozone, he freezing the water out of the air, but apparently needed a small kick-start of water due to his recent escape from the burning building. He only drinks a sip of water, but there is least a gallon of ice shown in the next scene.
In the final battle with the Omnidroid, Frozone produces large quantities of ice, maybe 100-1000 cubic meters at a time. Again, flow rates are meaningless, the water is not coming from Frozone.
The movie shows Frozone using ice for travel by skating on the generated ice, structural material by forming bridges and encasing the Omnidroid, and fire-fighting. Presumably Frozone could just about anything you could image with ice, dropping a wall of ice on somebody, creating ice handcuffs to hold for a few minutes, barricades, freezing vehicles to prevent starting. If Frozone can elect to generate much colder temperature, other uses are possible. Very cold ice is more like granite, very strong and not slippery at all.
For other suggestions re: using your cryokenetic power visit the Ice Manipulation page of the SuperPower Wiki
Finding online references for stopping power of ice was surprisingly hard (I kept finding braking distance for cars on ice). I gave up finding a perfect reference, but I did find army testing that included penetration in various densities of snow, Projectile and Fragment Penetration in Snow and Frozen Soil. In contains a graph, figure 12 on page 12 of the report that summarizes tests with 5.56mm, 7.62 mm and 50 cal rounds. The trend is consistent, denser (less air) means quicker stopping and even at 50% air all 3 rounds were stopped within 1 meter (39.37 inches). The only solid ice tests I could find online where not careful studies using solid ice. I did not find anything inconsistent with my original 3 foot claim (admittedly from memory). The army data is suggestive that my 3 foot claim likely was pessimistic for the stopping distance in ice. On reflection, my memory may simply be based on the Army study.
I might add that the army is more interested in the the armor afforded by snow than ice, because you can easily shovel (or plow) some snow barricades into existence.
I did some additional research on ice strength at -40 degrees. Found data suggesting that 3 to 5 times harder at -40 is more realistic. Presumably this is due to variations in how the ice was frozen, may be air embedded, whether it was same temperature throughout, etc. as well as different in the type of strength test. E.g.., static vs dynamic load.
BTW, how realistic is this? No, it is not realistic at all. Adding heat at a high rate is not too difficult, removing heat at a high rate is much more difficult. Unless you can pump water and liquid nitrogen (or such-like) in such a way that the nitrogen impacts the water when it reaches the desired location in a manner similar to a set of 3D printers I can't image how you could create the desired effect. Even this would not be as flexible as Frozone. The energy and mass requires would be incredible to produce the large quantities of ice that he uses.
To simply freeze 1 gallon of water that is just above freezing requires a lot of energy. 1 gallon H2O is 3.785 kg at 334 J/g (heat of fusion) is 1.264 MJ. A 4000 pound vehicle travelling at 80 mph has about the same energy. For his larger ice constructs, Frozone would need more energy than a fully fueled Airbus A330-300.
Such energy flows are compatible with a living person? So no, it is not realistic. Any any superpowers realistic?