T4i to 6D

For video the 24-105 has IS, which is a significant factor. The 6D silent shutter is useful for noise-sensitive situations or candid shots.

For interviews or public speakers, I often use the Canon WMV-1 bluetooth wireless mic, it's only about $200 and works nearly as well as my pro Sennheiser lav kit. It's less discreet but clips and unclips rapidly:

http://www.bhphotovideo.com/c/search?Ntt=canon+wmv-1&N=0&InitialSearch=yes&sts=ma&Top+Nav-Search=

I use a wireless mic more often than the Rode Video Mic Pro or external Rode NTG-2 shotgun mic. Camera-mounted shotgun mics are affected by room acoustics, and a boom-operated mic requires a person and it's easy to spoil a shot due to mic in frame.

For video you generally need manual focus. It can be done without a follow focus or viewfinder aid, although those help -- especially if you are young and have good close vision.

The lack of flash on the 5D3 doesn't bother me, as I'm usually doing event shooting in light sensitive situations. It would occasionally help for daylight fill cases, but I don't miss it.

Later you could get a 70-200 f/4; it's not that expensive and produces good results. The 2.8 produces amazing images (video and stills) but it's big, heavy and expensive.