Any advice so I'm not scared to arbitrage markets that can still lose me mana?
If you're spending a lot of time here then it's easy to see that there is a lot of low-hanging fruit. You bet on the low-hanging fruit and see the number go up. It's a time-value-of-money phenomenon: You get a higher yield wandering around until you see the low-hanging fruit and just pick it up. Longer-term investments like arbitraging something that won't resolve until the end of the year doesn't feel as good and is riskier. The only cure for this is to give yourself a time budget for fucking around on Manifold and have days where you don't check it. At least that's how I'm trying to avoid the same thing.
Oh, and you can make more markets about things you're genuinely unsure about and then bet on them to calibrate yourself.