1) Can have up to 3 individual switches in a single outlet. 2) Can work with just a single hot wire (no neutral). 3) Can be queried about it's status (on/off) back to the gateway.
There are a bunch of Chinese ones that meet 1 and 2. But I haven't found 3 so far.
I am planning to get some Z-wave light switches for my 3-ways (Zooz seems to make the switches that work the way I want).
1) Can you clarify this question - I'm not sure I understand what you're talking about. By outlet are you referring to a junction box or an electrical outlet (plug)?
2) Wemos require hot, neutral and ground. AFAIK, most smart switches at the very least want a neutral wire.
3) Wemos don't need a gateway (wifi), but they know their status.
If I could do it all over again, I probably would have skipped Wemo and went with Zwave instead.
The neutral wire requirement is really a killer for me, as I'm not going to rewire me entire house. There are some switches that only require the hot wire (they pass a very small load to the light, but not enough to lit up even very efficient leds).
As of the gateway I don't really care the interface. I'm prepared to write code myself or whatever is needed.
Are you sure you don't have a neutral wire in the junction box? In my junction boxes, the neutral wires weren't used for the old school switches but are capped in the back of the junction box.
Regarding the interface, the Wemos are not very reliable because they are wifi. I used to use X10 and they were way more robust than the Wemos. You might want to check X10 if you're going to code yourself. The hardware tends to be a lot cheaper than the newer switches.