You can certainly make music without needing more VSTs, but you will probably want at least a few.
Sylenth is certainly a popular standard (if getting a bit long in the tooth). The VSTs you want will depend very much on what kinds of sounds you want.
One of the more powerful that you can get right now is “Serum,” which makes some seriously crunchy sounds, but is a bit complicated (but totally worth learning).
Another of the popular standards that is starting to age a little bit (but still has a lot of usefulness left in it) is Massive from Native Instruments.
You probably wouldn’t want/need both Serum and Massive… I would take Serum over Massive at this point, you can make some CRAZY good sounds with it if you spend the time to poke and prod at it long enough.
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