Advice on wiring up a grow room microcontroller.

[FiguringOutLife]

I'm currently building a grow room microcontroller for my startup business and have come to the part where I have to wire up the high voltage side of my system.
Before I make some dodgy wiring and blow myself up I'd like to get some advice from someone with an actual qualification ?
What I've got so far is a microcontroller that switches on and off a series of relays depending on temperature and humidity.
These relays will be wired up to (at this stage) 4 standard wall sockets with a heater, a fan, a dehumidifier, and potentially a humidifier(not sure if I'll need this one).
Only 2 of the 4 appliances should ever be running at one time.

My questions are:
As I'm building this in a metal box should the box itself be grounded?
If so, how would you recommend doing it?
Are there any improvements you would recommend to my wiring?
How can I provide power to my microcontroller without the cowboy style jam it in and screw it tight USB charger setup?

If you can see any concerns that I've overlooked feel free to point them out and suggest fixes.

Photos of my current build with low voltage(microcontroller/sensors) side removed for less cluttered photos:

 

[FiguringOutLife]

Good advice, wrong plant

Make sure you use filters or you'll arouse suspicion with the neighbours...???

I feel like it's appropriate, so here's a pic of my plants ??