Everytime I custom create a rollercoaster, the excitement levels are always really low (usually around the 0.2 mark) whereas intensity and nausea are closer to 20! Anyway to solve this or hints for high excitement coasters?

Too high intensity caps the excitement quite brutally, fix INT before you even start working on EX. Right now you can't see the "real" excitement value, it might not be too bad once people don't fear for their lives anymore. Nausea will get better from doing that too. Start by watching a train on the G-force tab, fix the places where the graph spikes worst. Make it duller, slower, bank all curves if the coaster type lets you, less inversions, even simply ride length adds up.

Others already wrote about this in detail

Be cautious with tips from this wiki, it seems mostly written by beginners, rarely outright wrong but often far from optimal.

Once you got intensity down to no more than very high, preferably even less, this article has many good ideas how to squeeze the most excitement into the coaster. But not now, with ultra-extreme INT this will not help.