Algorithm creation is something of an expert-level task, so we have little basic information. If you haven't already, try the following:

Programming Manual for Harmonizers

https://www.eventideaudio.com/downloader/1007

Omnipressor: Anatomy of a Preset

https://www.eventideaudio.com/downloader/7340

Once you have moved on from these, try picking a few factory presets that look useful, and take them apart and see how they work.

Your synthesizer should be do-able, with PITCHDETECT, OSCILLATOR and MIXER. But, the skill will be in making it playable.