1. Adding a TC causes slower AF, intentionally based on the camera's firmware. A 1.4x slows movement of the focusing group by 50%, a 2x slows it by 75%. It's not as bad as it sounds, because with the TC mounted, the focusing group doesn't need to physically move as far. Still, it's usually noticable in practice with all but the fastest-focusing lenses.
2. It will likely speed up AF lock a little bit, newer models generally have improved AF algorithms, and the addition of metering data used by the 7DII may help as well.
3. I don't believe IS slows down Af lock, if anything it would speed it up to the extent that it provides a more stable image to the AF system. When shooting BIF, a fast shutter speed is usually required – fast enough to reduce or eliminate the benefit of IS. Leaving it on at high shutter speeds shows no effect on IQ with the lenses I've tested (but that does not include the 300/4L IS, and that lens has an early IS system that's not tripod sensing and may behave 'worse' than more recent iterations of Canon's IS). You can mount the camera on a tripod, use a fast shutter speed with and without IS engaged and test it yourself.
Hope that helps...