To expand on avantronica’s answer:
It sounds like you want a similar setup to mine. Midi from keyboard to OT. Midi out from OT to synth. Midi data received by the OT is passed on to midi out if you want it to, so the synth receives both the channel I play live on my keyboard and my sequenced OT midi channels.

The midi sequencer on the OT is a step sequencer, though, and have some limitations. You can’t record gradually changing CC values, for instance. It would end up as one value per step.

I have a project that I use as a “template” with all my usual settings, including midi channels etc. Whenever I start something new I load that project, save it with a new name and use that so I don’t mess up the template. However, the OctaTrack has an Arranger mode where you can set the tempo for various patterns. So I think the arranger would work well for what you want to do with many songs in one project.