Building a small is definitely challenging but you can do a lot with it if you plan things carefully. You definitely want a balance of voices, modulations and control, so try to find modules that have multiple modes/uses, have built in VCAs or even filters.
I think you can ditch the Arp and Tune since the Hermod will cover those areas for you, so will Pam's Workout. You might want to add another voice source - maybe a 2hp VCO, Pluck or one of the Erica Synths Pico series voicing modules. In my opinion, the Expert Sleepers Disting Mk4 is an absolute essential in smaller systems providing you a plethora of tools that will come in handy including VCOs, filters, sample playback, the list goes on and on... If you don't mind digital VCOs, the Klavis Twin Waves might be a good oscillator that could help you add more voicing options to the system instead of Plaits. That will also free up a few hp that will help you fit other stuff in. Also take a look at the Mystic Circuits 0hp line. These are literally 0hp and highly usable for any size system and dirt cheap too!