Powering 5v 1.1a solenoids

I am trying to figure out how much three solenoids will require.

I am using a MOSFET to control the solenoids ( Mini Push-Pull Solenoid - 5V : ID 2776 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits ) from the arduino but I need a separate power supply for the solenoids.

Was looking at something like this:
https://www.amazon.co.uk/AC100-240V-Transformers-Wireless-Connector-5-5mmx2-1mm-5V-6A-30W/dp/B07P8KR2FJ/ref=sr_1_3?keywords=5v+6a+power+supply&qid=1572610779&sr=8-3

On top of that, could I also provide power to the arduino via USB to mains? Or should I use the barrel DC connector?

3x 1.1A = 3.3A.

You can probably use the same 5V to power the Arduino. Use the 5V pin, that's what it really is for.

DO NOT power from the Arduino, it can only supply a hundred mills or so. You need another power supply, the one you linked to is adequate. You can then use a mosfet or relay module to drive the solenoide. If you use a properly rated avalanche rated MOSFET you will not need the clamp diode.
Good Luck & Have Fun!
Gil