Multiplayer Plan

As a newbie programmer I might be/know I am getting over my head with trying to jump right into multiplayer. However, If I was to create something and then wanted to make it multiplayer would the work be A LOT harder then starting out programming as multiplayer?

As of right now I followed this :How to create an online multiplayer game with Unity - Paladin Studios

But it may be outdated? As a start however I was able to create players and have them run around, trying to move forward with other things has left me confused. Although without the multiplayer aspect I feel like I can get things done, whether or not they are proper concerns me, but as stated I am a newbie.

What do you think?
Is there a more updated multiplayer starter guide(provided that one is in fact outdated)?
Would it be wise to continue as I am now, and then worry about the multiplayer part later?

Thanks.

P.S Not sure if this was the right place to ask this, sorry in advance if it is not.

It’s still mostly valid for PUN. It’s not all that useful for uNET.

yes it is harder to implement multiplayer afterwards.
I find this a good introduction: