Sciences PI Plate

Hi every ones,

I'm a young engenner in plant biotechnology. On my free time i try to create an open source plate for the Raspberry pi which has lots of functionality very usefull for science project (Plant growing, Invitro cell, hydroponic control, compotemental study...)

I'm really a beginer in electronics, but i read a lot electronic book, looking schematic and see video.

This plate have :

-8x relay 220V 5A control by a Darlington Array
-8x Analog input
-4x BNC connector connect to 4 Atlas Scientific Stamp (Ph, EC, DO...)
-RTC clock (to be sure of time when data are store on database)
-LCD screen 16x2 to facilite the reading without computer
-This project will come with backend/frontend distribution

Before i order all parts and PCB, i wondering if you be able to check my schematic to validate it and maybe improve it  :P

Schematic Image files (2Mo)
Fritzing file FZZ

I have few question too  :

1/ Can i connect all my ICs and LCD to my external power supply, i read on internet this is better than connect on the 5V from the Raspberry PI?

2/ If i connect all 5V on my external supply how many amps i have to provide (the sum of all amps require by parts)?

3/ Do you know an I2C IC can replace the 74HC4052 to make all the plate in I2C and made it usable by more than a Raspberry PI ? (if it interesting)

4/ Which width is recommand for the wire on my pcb 24 mil (or smaller), and for the 220V Relay the biggest ??

Thanks you for your help, and your website !
Regards Erwan

Picture of Sciences PI Plate