Some of the greatest guitarists in history developed their talent and their style without any pedals at all. It was discipline, practice, desire, and talent that got them great.
Music has changed and nowadays I agree that there is some need for more electronics than just a guitar can provide. But it's still a good idea to develope and learn without the aid OR hinderance of extra devices. We tend to rely too much on effects and less on ability/talent.
That being said.....
A good tuner is essential, not only for keeping the guitar in tune, but also for ear training. You need to know what the correct note is before you can hear it in your mind.
An OD pedal can do so much for your tone and is so easy to learn how to use that I think this is a no-brainer addition to his arsenal.
Reverb is nice but not essential. I played in bands for 5 - 10 years without reverb and I did just fine. You don't say what amp he is using, but most beginner amps have this built-in so I'm going to assume that this is a non-issue.
A wah pedal is not necessary at all, especially when first starting out. But mostly because it takes a lot of practice to get good sounds from a wah and I think his time is better spent learning the guitar rather than learning to use a pedal with very limited application.
A volume pedal was one of my first pedals and it got used alot. Constantly. Is it important? Necessary? Probably not. Useful? Maybe. It is an indespensible part of my rig because I use it mainly to balance my amps in a stereo rig with each amp having different settings and effects. Complicated, but the tone is worth it. I use the volume knob on my guitar to adjust the gain or to clean up the sound.
Encourage him to keep it simple. Become a master of the instrument, then all else falls into place. Effects can be gradually added as the need arises.
Just my two cents worth from an old-timer.
