Thanks for the feedback. Synonyms is on the immediate roadmap, but not available at the moment.

Is it also possible to control typo sensitivity

You can control overall number of typose with ?num_typos=1 -- there is no way to define min chars for a specific typo. The engine does make some intelligent decisions to optimize. For example, for a 2 letter query it does not use a num_typos=2 even if that is specified.

Glad to hear about the setup. Will continue to improve.