My current database has only 9 sentences (I think).
I'll upload another database with 180 sentences today. (I'm almost done)
More sentences will produce more possible combinations... but it's still not really satisfying. I think you're on the wrong track here.
Instead of combining pre-fab sentences to create a readable paragraph, try to construct a story "framework" from basic elements. (Don't worry about readability -- you can flesh it out later.)1. establish a scene/situation
You can still use random elements to fabricate a situation. Like a person driving through town, or a couple on vacation, or two people exploring a cave. This part can be random.2. introduce conflict / tension
Your conflict can still have some randomness, but choose it based on some element of the "situation". For example, for people driving through town, you could have someone become ill/die, or be kidnapped. For an outdoor setting you could have some natural disaster, or have someone get lost. Or introduce an antagonist, or some unexpected "object".3. built action to a climax
The types of action can be random, but they must be linked to the situation and conflict in steps (1) and (2). For example, your "action elements" could be running away, searching, hiding, fighting, etc. But the details are linked to (1) and (2).4. resolve the conflict
Again you can have random outcomes / resolutions, but they must be related to the same action chosen for (3). For example, if your action in (3) was fighting, the outcome can be winning, losing, escaping. If your action in (3) was searching, your outcome can be finding, getting lost and dying, giving up.
Basically you're using a branching structure. But the only truly random details are the elements chosen in step (1). After that, the branches are limited to what makes sense for those particular details. So as the story progress, the randomness becomes more structured.
Granted, I haven't thought about exactly how to do this. But I think it's a better approach.