What do you suggest is a good way to make the Main Menu Level more interesting?
-Do you like to add landscape and lighting? How can I keep the level at low cost in realtime?
-Alternatively, How do you like the idea of running a rendered movie with an overlay for the GUI.
-If you have any other suggestions I’d like to hear them.
I’m not a Houdini pro but I’m starting to fall in love with the render looks. “Multiplayer, Anime Inspired, Story Driven Gameplay.”
These are pretty nice
That reminds me of the Lyra Demo! Super cool!
My main menus are always a separate map, so you can do anything you want to.
You are trying to build a mood for the player so adding elements that make your product more exciting and interesting the better. You want people to see it and get hyped they are on the main menu waiting to press the play button. Could be a black void with cool music with some simple text animation. Could be a full CG movie or real time movie.
What I like to do is make a real time movie that loops using the assets I created for the game that does not take a lot of resources but has the goal of building the mood. When I create a class I will create a toggle for cinematic mode so I can reuse the exact same asset for this purpose.
I also have used it as a track mode like old arcade games where I offer hints and information about the game so if you click the button and walk away from the keyboard come back you might come back at 50 second mark which is showing you a cool thing you didn’t know about the game.
In my past Project I had the Main Menu Level being a half-pipe ramp to test your actual Camera Settings so basically you was able to see the Level, your Car and the Camera Setup directly in the UMG 
Additionally I have made a mini Music Player and video-based Level Preview before you play so you could see how the Level looks like 
One of cool ideas from a Discord mate was that you have to walk over with your Character to a PC where you could see the Menu Options like Start Game, Settings, Quit and so on
There are many possibilities, it pretty depends on what your game is but there are plenty of ways to make it look more fun
And to answer (at least some of) your questions:
-Having a Landscape or any kind of Level as Main Menu - that’s a nice addition to a game, feels better at the very beginning
Low Cost? Just don’t make it too big
How do you like the idea of running a rendered movie with an overlay for the GUI.
Personally - I love it 
Here’s how the Main Menu looks like in my old good (but crappy) game called “Car Madness” including the Features I mentioned above