What Jim said if you happen to be able to afford proper Mutable instruments modules, buy them, as its a nice thing to do.
I'm particularly enjoying Marbles as the main control in my rack, feels like the glue you can hold a bunch of different parts together with :) (other MI modules I own are, Links, Kinks (On Jims Advice), and Veils). I own a Monsoon version of Clouds though.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.