Not sure what you meant here, but the 5D3 does let you see what you are focusing and then once focus is locked, the whole viewfiender flashes red.
Nope. Not in AI Servo... which is quite possibly the main point or one of the key points of the much improved AF system, being able to track and shoot action (which the 5DC and 5DII aren't all that great at).
7D works the same way... and I'm sure the 1DX will too. Any camera with the active matrix, transmissive LCD "Intelligent Viewfinder" has to work this way.
All you see is the gray box or boxes of the active AF points. If you are using USM lenses, you can throw the lens out of focus manually and see it snap back. But often there isn't time for that with moving subjects. So you just have to learn to trust the camera and yourself. It takes some getting used to.
In One Shot, yes you do get the "red flash" and the green LED of focus confirmation once focus locks onto the stationary subject.
Other cameras with the "simpler" AF systems that display all the AF points all the time, in AI Servo the camera will light up the selected AF point red momentarily when focus starts, but also don't show "lock". (AI Servo never locks, it's continuously updating to track the moving target. In AI Servo the camera can't give Focus Confirmation... there's nothing to confirm.)
Actually, the AI Servo "flash" to show AF start at the selected point or points isn't needed in the transmissive LCD cameras, because you can set the cameras up to only show the active AF points. If you have a multipoint mode selected, only the ones the camera is using at the moment will display, and if the selected points change while tracking, you'll see the displayed points changing to reflect that.
It can be difficult in low light to see the active AF boxes in the 7D (and 5DIII, 1DX I'm sure) viewfinder. There is a "viewfinder illumination" setting available, that makes everything glow red. It's a bit obnoxious, so might not want to use it all the time.
As to the overall and original questions...
OP has $5000-6000 budget and is dead set on putting most of it into the camera body, no matter what. Realistically, in order to work weddings and portraits, I'd estimate between $12,000 and $15,000 would be needed to put together a minimal lens kit, pair of cameras and a minimal location lighting kit. This estimate is based upon switching from crop to FF with 5DIII. The range is the difference between getting one 5DII and backing it up with 60D, or instead getting two 5DIIs. Alternatively, a similar kit could be put together around two 60D (adding one) and using other items already on hand, for about $7000.
But, OP is determined to get the 5DIII come hell or high water, so it's all pretty much a moot point.
