To address your initial question, the Arduino board has a voltage regulator- for ITSELF !
It’s not really intended to power much more off the board, other than a couple of LEDs, pull-ups etc.
To drive anything substantial with the Arduino, you need to consider your [whole power supply as a mini project in itself].
@Johan_Ha mentioned one approach, but you need to plan a bit, because 150 LED junctions will draw a bit of current in themselves (50x RGB x 15mA= 750mA)
Six (valve) solenoids, which could have a pull-in current of 150mA each, or solenoid (actuators) could draw even more at their rated voltages... (6x 150mA = 900 mA or more)... Your relays will add to that...Read about drivers.
All these MUST be isolated and filtered from the Arduino supply, otherwise you’ll end up with unexpected ‘resets’ and other behaviour.
Also keep track of your 0V/Ground wiring, and any 3.3V and 5V components.
Go read some of the ‘Introductory Tutorials’ section .
It’s fun, but daunting when you first start.