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as everyone else has said - larger case

these 'beauty cases' are great for specific purposes once you know what you are doing, but as a beginner you don't have a clue, to be honest they hint at a lack of research - particularly not reading a lot of the thousands of newbie posts (here, reddit and muffwiggler for example) - because almost every single one says GET A BIGGER CASE if the OP is asking about 'beauty cases'

with regards to the case - both the mantis and the lc9 are great value for money - one thing to watch out for is that if you think you might want to get high power consumption modules (metasonic, for example, or video) in the future is that the mantis has a lot more +12v available than the lc9 - -12v are the same iirc - for most people this may not be an issue, and you can always add an extra psu if you need

the only sensible advice to take in modular, is to buy a bigger case than you think you need, buy fewer modules than you want and grow slowly = there is no need whatsoever to fill the case immediately

just get the absolute minimum (sound source, sound modifier, modulation source, way to play, way to listen)
if you have money left over then the following modules (or similar) are very useful additions - links, kinks, disting, shades, a quad cascading vca (veils perhaps) - the last one may be (should be) your way to listen from above

from a learning perspective Maths is my modulation source of choice to recommend to beginners - it's complex, but only because it has a few different sections - but the illustrated manual is an excellent modular tutorial in itself - work your way through the patches in it a few times and you will know a lot more about modular synthesis than you did before

play with that for a month or 2 and try to work out what you are missing - disting is a great help here - and then buy another module (or 2 at most) and repeat and repeat and repeat etc etc