Hi there
You will need more space sooner than later :-)
I just finished my first rack about 1 month ago. I see you are interested in the Mantis.
I also have the Mantis and it's already full. So when i want to try a new module i have to get rid of an other module (that's stupid)
Tiptop Audio will release a dual Mantis Bracket later this month. So you can mount another Mantis case on Top.
Thats probably the way i will go in the near future.
What I realizes so far is that I don't really like small Modules. I've got a Monsoon Clouds but i would prefer the Original Clouds.
(Modules like the 2hp Pluck and the Arp are ok)
I also have the Erica Synth Dual FX. But i don't like it that much. I would prefer a nice delay Module like the 4MS DLD and for Reverb something like the Erbe Verb. Both of these Modules are 20HP. I need more Space.