Good audio lasts for years, so buying a solid microphone bundle upfront keeps you from upgrading twice. You want a setup that handles a noisy room and holds up through hundreds of hours of recording.
Spring is the sweet spot for audio gear. Manufacturers drop rebates then, and last year's flagship models usually go on sale right before new revisions hit the shelves.
An intro window is a firm payoff deadline, not free money. If you still have a balance left after 18 months, regular interest rates kick in on the remainder, so stick to your $25.00 monthly schedule.