Hello Dario,
it depends
For sensors, it is probably best to use the http API and have the node upload its data to easyIoT server. For actors like relay or MOSFET, it is better to use automation program.
I have been very busy with real life work lately, but plan to do something with DS18B20 sensors in the coming weeks, most probably using the HTTP API to update virtual nodes from the sensor directly/without polling it, as shown by easyIoT in his door switch example.
Also I just "discovered" that some smart people added esp8266 support to arduino IDE (so one can write code in arduino C instead of Lua, also use classic arduino libs like dallastemperature or DHT11), and I'll try this too.
Also, I designed some experiment PCB for esp8266-01 modules and ordered 10 pcs from china, and they look pretty good quality-wise, and even work as expected - with up to two MOSFETs, FW programming jumper, UART incl. level shifter, and both GPIOs broken out as connectors, one of them optionally for 1-wire too, if pullup resistor is soldered.
About SWITCH button: yes, intended use is with MOSFET - it sets pwm duty cycle to zero or full, so the result is equivalent to switching a GPIO, and thus it SHOULD also work when a relay is connected instead of the MOSFET. But of course you could easily replace the pwm command with simple GPIO switching command in Lua.
edit - if you connect the mosfet sorce and drain to 5V it will also work, they can take up to 55V in case of IRLZ44N mosfet for example. But you can use simple transistor to switch 5V for the relay, no need for mosfet when no dimming is needed (although it will work with one)
regards