Repeating characters could be a software problem (too) but a keyboard that wants more than 100mA might not be compatible with the PI, and there are more reasons for that than just that the PI is fused at 140mA
The problem is that the fuse will "eat" a large portion of the 5V, so for many USB devices there won't be enough left. The exception are official <100mA devices (AKA "single current unit devices", not to be mixed up with units actually drawing less than 100mA, yes I know its confusing
The simple rule is that the PI is only compatible with units that state implicitly in their documentation that they use less than 100mA
, such units are simple wired (and sometimes but not always wireless) keyboards and mice. That is about it! most WiFi dongles use more than 100mA, and also keyboards with built in trackpads, USB mouse connectors, or backlighted keys are normally not in the <100mA category!
If you want keyboard and mouse on one (1) USB port, the best solution is a bluetooth based adapter (using <100ma) with a wireless keyboard/mouse combo that has been tested and is listed as "known good" in the RPI-wiki.