This isn’t perfect but I got a lot of things working and I included links to the tutorials I followed. I hope this helps.
Thank you for your work, for “unifying” several good free things around into one menu system. Somebody had to do that! 
I dig single player games only, so, it fits for me. As we discussed in other place, menu for instant level choosing would be supper addition here. And (i did see in BPs you already planned this), second row of key/axis bindings could be great addition, I think.
It should be pretty simple to add a second row of keybinds, it’s just the same process as the other buttons. If you need help I’ll make a tutorial when I have time.
It is cool to name it “open source”, but unfortunately I couldn’t find there any sources, only blueprints…
I can not say what is right or wrong about naming, but, this menu system really =is= Blueprints only, and that’s the special beauty of it - clean thing. No plugins, or C++ parts, everything done in Blueprints. And free.
Yeah, but its ok to add [Blueprints] and [Free] to thread name, instead of “open source”, because its different things.
I would like to ask Author for small help. I really would like to try to add joystick axis recognized for remapping, for joysticks / flightsticks that are recognized by this free plugin:
GitHub - tsky1971/UEJoystickPlugin: Unofficial Joystick Plugin for the Unreal Engine (there are branches for all recent UE versions).
Short story: buttons from such plugin-recognized flightsticks are “felt” by remapping just fine, but axis are not, at all (but they work fine, if directly configured in Project Settings - Inputs). I feel like I have to add nodes to remapper, about these specific axis. Problem is, with my still limited experience, i am “running in circles” in your menu system remapper Blueprint, and can not really understand, what part takes new identified particular aixs input / axis name. Could you please point me to right nodes, variables in your system? Place where i can try to add additional input for recognition. Many thankyous in advance!
(P.S.: I am also going to try to remake your menu system for 4.19. Having it only for 4.21 is too restrictive).
P.P.S.: i add picture of BP nodes (that I know of) that this “Unofficial Joystick Plugin” has.
Hello again. I have more or less successfully added “Instant Action” direct level selection into your system. I used practically unchanged level selector by Rohit Kotiveetil:
It makes buttons list of levels that are marked “Unlocked” and “Has Gameplay”, can also display a scene screenshot
In your system, i added button “Instant Action” in my menu. It is working (I edited some things so that everything works within your Gamemode), mostly, I think return from levels is broken a bit. I might send you such extended version, if you would like to?
The recent update has a map selection menu in it
I know, I know, I noticed it (github updates) shortly after I made my own version, hehe 
Thank You for adding that direct map launching!
What I am investigating now (or, rather, “fighting for with little knowledge”) is - to have axis recognized for remapping, if device is added thru this free plugin:
Joysticks thru this plugin go directly into lists in Project Settings - Inputs. Buttons are also seen by remappers. Remapper does not “feel” axis moved. I think there is a need to make some kind of new node, “Axis moved”, with key structure as output. I would really, REALLY (small Paypal maybe) appreciate some creative help from experienced people.
Here is a screen of nodes that this plugin does have:
