If you get empty custom/filtered decks created from your tags, there's probably something wrong with the search, which you can check in the deck options for the custom deck. For a single tag you'll only need something like tag:Spanish1 in the search field, make sure there's nothing else in it. You can also try out the search in the card browser to make sure it returns the desired cards.
I'd recommend adding all words to one single deck and tag them by the groups you want to have, this gives you the most flexibility. You can then study any combination of groups and it's no problem to have overlapping groups. If you put everything into individual decks, they'll be very small and the contents predictable (if you have to do that, at least use subdecks).
Eginhard