How many cards? and how long a game?

Is there a reason why you can only have one word per card?
Almost every similar example I can think of has multiple entries per card (although admittedly Apples to Apples only has one word per card: but that's a slightly special case in that the cards have to be handed in so you can't have more than one per card.)

Game-length? An artificial limit that can be used to cap the game but not force it to end sounds the best idea. Again, look at Apples to Apples for an example - although it has a game end criteria (when a player has collected a certain number of cards), it often goes on as long as people want to carry on playing.

As for dictionaries? There are a number of computer wordlists around that might be useful, but it sounds as though you are probably on your own with this one since you are the only person that knows what the criteria you need to select them with is... Sorry that isn't very helpful, I know.

Tokens as a game-ending device are good if they have a place in the game. If they only exist as a scoring/timing device, then it can be a nuisance from a production perspective; although having a specific scoring mechanic other than pencil and paper is good, having one that is otherwise just an extra component is probably bad. (See my reference to Apples to Apples again, in which the scoring mechanism is one of the card types. I'm guessing that you can't do that with your game, that more than one player can score points off a single card.)

I see your issue with the words on the cards: multiple potential words could cause confusion. OTOH there are probably fairly simple ways around that: have four words in different colours and ask people to work on the word in a particular colour etc.

If the game requires a certain amount of concentration then you probably have to reduce the length, especially if it's a game in which everybody is playing all the time. This is even more so if each round is similar in style.