Todd is correct; You can make a decent puzzle with just 75K, and many lists extend into the 100's of K. (And I'm convinced that if you have the Cruciverb wordlist, then you probably have access to 99% of the entries that you'll ever need which are shorter than 7-letters ... the longer, multi-word entries are the ones that you need to go out and locate from whatever source you can). A more important issue is how well ranked one's wordlist is, and a beginner can rerank enough words in his wordlist to produce publishable puzzles. If you have the Professional version of Crossword Compiler, for instance, you can adjust the ranks of words that show up in the fill menus ... and that helps immensely. Something to think about.
I have dozens of wordlists which function in different ways. For instance, if you were going to make a puzzle in which none of the entries contain the letter E, then you would go to the Word List Manager (in CC) and figure out a way to produce such a wordlist. (How else would one make such a puzzle?) I also periodically make wordlists which contain entries of all the same rank or the same word length ... just so I can make visual inspections and adjust them accordingly. (Think about it: words only compete with other words which are the same length). One could also make mini-wordlists that are all Roman numerals -- things like that -- so that their ranks could be adjusted quickly before adding them back to the main list.
One other thing I recommend: have a separate wordlist which contains theme-specific entries, and use that wordlist to periodically purge such entries from your main wordlist. Whenever you download an upgraded version of the Cruciverb wordlist, you tend to pick up more theme-specific words, so identify these and add them to your purge list.