Hey @MattAV26! Welcome to the forums!
This one is saying the problem is actually the actor array that it’s not managing to get. What’s likely happening is the “Get all actors of class” hasn’t finished yet and can’t give a return because it hasn’t scanned the entire level quite yet. Try throwing a delay there before the spawn, say delay 0.1 and see if it fixes it. If so, you may want to consider a different spawning tactic, such as the level blueprint doing the work for this.
For this one, I believe you need to do the same, do a bit of a wait. You need to assign it to an owning player, as well, as it looks as if you’re doing a multiplayer game?
But yeah it’s accessing none because SOMETHING is not finished getting ready before the Add To Viewport is called. Typically UI is instant, so it is likely the character is not spawned, and a controller not assigned.
Try “Get Player Controller” for the owner, or whatever it is that the Add To Viewport asks for (mouse over the input node, then search for “Get ____”, whatever it wants it’ll likely work)
Hope that helps, let us know how it goes!! 
Edit: For the widgets I saw that these are level opening buttons, try adding to viewport AFTER loading the level! It looks like you’re trying to do this at the same time.