Learn German: Das Tempolimit ist hier ja sehr niedrig, also riskierst du ein Bußgeld. - The speed limit is very low here, you know, so you are risking a fine.

In German, also is a false friend. It means "so" or "therefore," not "also/too" (which would be auch). Here, it acts as an adverb taking up the first position in the second clause. This forces the verb riskierst into the second position, right before the subject du.

What is the purpose of ja in this sentence? Can I just leave it out?

You could leave it out and the grammar would be fine, but you'd lose a subtle nuance. Here, ja is a modal particle used to show that the speaker assumes the listener already knows this fact (often translated as "you know" or "as you know"). It makes the statement sound more conversational and collaborative.

What is the difference between ein Bußgeld and eine Strafe?

Die Strafe is a broad word for any "punishment" or "penalty" (ranging from prison time to a parent grounding a child). Das Bußgeld (from die Buße meaning "penance," and das Geld meaning "money") refers strictly to a monetary fine. It is the standard term for traffic tickets and minor administrative offenses.

Is Tempolimit the standard word for "speed limit", or is there a more traditional German word?