Yes, it is possible that large discrepancies in the subtest scores might suggest interfering factors, such as learning disabilities.

The GAI is calculated the same way as the FSIQ; it just doesn't include the WMI and PSI subtests.

The WAIS-IV composite scores are unweighted. There are other tests that are weighted, such as the Woodcock-Johnson (WJIV, currently).

...pronounced like the long vowel and first letter of the alphabet...