Grouping words in categories is good and natural idea while creating new language.
For my new dialect I split Swadesh 200+ list in categories: Pronouns, Conjugation & participles & prepositions, Numbers, Adjectives (quantity, size, colors and other), Persons & relatives, animals, plants, parts of body & organs, verbs, cosmic objects (like Moon and Sun), terrain types & objects, weather & fall-outs, fire, time & seasons. Then I expanded this list a little bit in each category.
The next step is to translate elvish, mannish, dwarven etc. names for Arda-specific geographical terms (specially places of Mordor), names of races, creatures, animals and plants.
Next are the words for orcish (or just dark) way of life (kill & destroy). However there are already plenty of them in Svartiska. Which brings names of weapons and armor, and then names of crafting materials (specially lacking words for metals), technological processes (casting, melting, forging, hardening etc.), cooking (speacially meat in field conditions), names for professions etc. Words for killing & destroying also brings us more terms in anatomy and parts of body.
Then goes roleplay terms from LARP to D&D.
The last step will be dialectical words for Orcs from different regions (Mordor, Moria)
Each step leads to word-making process in other categories.
I hope this approach will make dictionary small but vivid and is better than trying to translate some random assorted texts. Perfection will be achieved when we will be able to translate dialogues from LOTR without much simplification (like Shagrat and Gorbag conversations on Horngoth's page).