A Cluster of wifi sensors

Hi Forum,
I am starting a new project and would like to use this forum as part of my back up team.
The project involves the following:

a) A main control unit. (Mega2560 with wifi communication via ESP 01)

b) Remote sensors to measure Humidity and temperature. (AM2302/DHT22) Communication must be
with
wifi (ESP 01).
A remote string of sensors to measure temperature (DS18B20) They will be in a string connected and
will communicate with a Uno via I2C.

c) A mains switching board that is controlled by a Uno via wifi (ESP 01)

The Mega2560 must be able to send data to a PC for data logging.

Firstly,
I have some experience in programming but I am afraid this is my first wifi project.

And secondly,
I do this as my hobby, so progress might be slow and replies may take a while.

Any help will be greatly appreciated.

TheBrain:
A remote string of sensors to measure temperature (DS18B20) They will be in a string connected and will communicate with a Uno via I2C.

This is incompletely incoherent and, even if feasible, is almost certainly a really bad idea.

There appears to be nothing you have said that justifies a Mega or a Uno. You can probably do all you need with ESP8266s of one sort or another

Indeed - a single NodeMCU or WeMOS mini will be able to do the same as an Uno/ESP01 combo and much easier to program.

How do you plan the communication to the computer? A Mega can easily send stuff to a computer over the USB interface; a NodeMCU or WeMOS mini gives you a choice of USB or WiFi; and with expansion boards there are a whole host of other options.

Also you have to describe/sketch your sensor clusters much better as I have no idea what you're trying to do, really.