Great stuff, and a 20” front wheel is fine for audax. You can get tubeless fast tyres (pro ones) if you want a little extra speed, same for back, with suitable rims. Main way to get faster is simply to commit to riding your new recumbent majority of time to develop the legs etc.
I used Contact Urban 32-406 on front on my P-38 for all my audaxes up to 1,000km. But I’m recently on pro one tubeless, having sourced tubeless rims and built up a tubeless dynamo wheel. They do roll faster based on my rides so far.
I’m no slower than road bike over audax distance, even ones with hills, taking in Chilterns, Cotswolds, Wales etc. This is only after committing to making my recumbent my bike of choice for vast majority of my riding. When I rode it occasionally that wasn’t happening.