(I’ve moved this to projects so you can get individualized responses based on your own set up.)
You’ve obviously done a lot of research, and you covered most of the basic approaches. 
One more option which has become very popular in the last six months is to add one of the smart switch covers. This is a device with its own buttons, battery powered, which fits directly over the existing switch. This allows you to leave the power always on to the smart bulbs, but have an intuitive switch right where people expect to switch to be without having to add another switch next to it and put a child lock on the original switch next to it.
These are discussed in the following FAQ, along with most of the other options that you mentioned.
The one thing that concerns me is your target of 500 ms of latency. Lutron, which is an engineering company that only does lighting, and holds a lot of patents, sets their target at 300 ms. But unfortunately they are not directly compatible with SmartThings. A cloud to cloud integration was recently announced, and is expected to be available in the next month or two, but because it’s cloud to cloud there may be an additional second or so of latency added.
Most of the Z wave switches say that their target is 500 ms, but that’s the best they hope to do and many are much closer to 1500 ms. Even up to two full seconds in a cloud-based system like smartthings
A Hue dimmer switch working with a Hue bridge and Hue brand bulbs, generally has very low latency, in the 400 to 600 ms range. But that’s when they are working directly, not going through SmartThings. They have been a lot of complaints about latency in the SmartThings/Hue integration in the last few months. That wouldn’t affect your Hue dimmer switch, because it’s going to work with the bridge, but it would affect lights that you had come on from a SmartThings – controlled device. So it kind of limits your options.
Since all of your bulbs are currently on the same circuit, it might be quite costly to have an electrician separate them. @Navat604 or one of the other electrician experts in the community could probably say more.
So… I guess my first question is is your 500 ms target just for the time it takes from the time someone physically presses a wall switch until the overhead light comes on? Or are you using the same target for other kinds of automations, such as when you unlock the front door or when you trigger a motion sensor or when you press the switch in another room?