The first issue is does the different fork match the old one's fit WRT to frame. Is the steerer the same diameter and headset fit? Will the new fork work in the frame/headset.


Second is how the new fork will change the handling, or not. Is the axle to crown race seat the same? Is the rake the same?


Third is if the new fork can accept the same accessories as the old did. Fenders, racks, lighting.


Nothing wrong with mixing brakes types on the same bike. But some brakes require a greater cable pull amount then others do. Canti brakes usually are paired with levers that pull a short amount of cable. Hub brakes (including many disk) require a longer cable pull. There are devices to translate cable pulls (The Travel Agent as example) but many feel that this solution is either overly complicated or not as effective as just getting a well matched system. What is a problem is when trying to run two brakes off of one lever. This is when the matching of cable pulls is really important. Even then this type of set up can be less effective then only having one brake on the lever. (Tandems come to mind)


Carbon forks tend to be very strong as far as how much stress they can handle but they also will fail in a catastrophic manor sometimes. They also can suffer from bonding issues, I've seen drop outs come loose as example. But these speak more to the build quality then the materials in play.


There are so many factors that contribute to the "feel" of one fork to another. When actually riding one can't separate out the fork's stiffness from the air pressure or profile of the tire, as example. Changes of A-C dimension and rake (and the resulting trail change) can't be separated from the change to the bike's front center. But do be assured you will feel some difference, just that exactly what that will be is hard to anticipate completely. Andy.