Is the TRBX605FM active or passive?

It is active with a 3-band EQ, and pulling the volume knob bypasses the preamp for a passive tone. That means it still works if the battery runs out.

How does it compare with the TRBX505?

The 605FM adds a flamed maple top and different body woods over the plainer 505. The electronics and neck layout are closely related, so the choice is mostly about looks and wood tone.

Is the 5-string neck hard to play?

It is wider than a 4-string, as any 5-string is, but the profile is slim and most owners adapt quickly. Try one first if you are moving up from a 4-string.

What strings does it ship with?

It comes strung from the factory with a standard 5-string set. Replace them with your preferred gauge once they wear out.

Does it need a battery?

Yes, one 9V battery powers the active preamp. The passive mode works without it.

Is it good for beginners?

It is more bass than a beginner needs, but it is easy to play and will last through years of progress. Beginners set on a 5-string will find it forgiving.