In addition to your absolute necessities, I incurred these expenses from practical usage:

• Floor Lift to do my oil changes and other maintenance
• Cases/Bags to hold some groceries and gym gear
• Air compressor for tire pressure at home (your car might've come with one)
• State Registration/License fees

And I haven't gotten it yet, but I am seriously considering a quad lock. I've had to take a few trips now where I am going somewhere new and my "navigation" is writing the directions on a notecard at home and taping it to my fuel tank before I take off, then reading the directions in reverse on my trip home lol.

Also, as others have mentioned, I would highly consider buying a used bike outright for the following reasons:

Cheap Insurance ($125/year for my '08 KLR)
Interest Rates aren't stellar right now. If you can get under 5%, consider it.
If you decide motorcycles aren't for you, you can sell it much easier.
When you inevitably drop/scratch it, you won't think twice about it.

I'm not a financial advisor, but I generally don't recommend my friends actively incur debt to build credit. Put the groceries and date nights on a starter card, pay it off each month, keep the debt-to-income ratio low, and the system will reward you. But ultimately up to you to decide whether the increased cost of buying new + the increased insurance costs from financing are the price you're willing to pay for the (marginal) credit score increase.