So I’m about to start my build stage and the session suggests 90 - 100rpm. I’ve also read that a straight chain line is optimal and one does not need to chain your gearing when ERG mode. The question, do I need/should I/ to change my gearing to enable a 100rpm target in my next session and should I be changing my gear just to hit a specific cadence range during a session.
Yep, erg mode will set power, regardless of your cadence.
A few things to consider…
chainline, impacts noise and wear
gear, impacts speed and noise
cadence, low cadence can have odd impact on power handling by trainer (not as consistent, sometimes tris to ramp power up and can be hard to maintain)
I run my trainer SS, so don’t have a choice. But when I ran geared, I picked a cog in the low-middle end of the cassette to minimize noise and flywheel speed.