Nice trike, great color! We also have a 2004 in Kelly Magenta Metallic (Honda's name for that color - the State of Missouri has it titled as "Purple") BTW, it is a 1 year only color for Gold Wings, therefore a rare and unusual color.
As far as the accessories, get a Custom Chrome, Big Bike Parts and a Kuryakyn catalog. Check out websites like CycleMax, Wingstuff, Chromeworld, etc. You'll soon be overwhelmed by the stuff you can put on a Goldwing. Oh, a high-limit credit card will be handy, too.
When we got our trike it had most of the stuff I would have added anyway. The only Must-Haves were some more lighting in the rear - I added Hyperlites and some red LED running/brake light strips - a set of Baker wind deflectors - hand wings, wind wings, and trike wings - and a Diamond Custom seat - we routinely do 400 - to 500 mile days, so the stock seat didn't work and Gloria found the passenger backrest uncomfortable.
And lastly for now, an unsolicited insurance tip. A 2004 stock Goldwing in excellent condition has a Kelly blue book value of about $6000 trade in and just over $9000 retail. Unless you get an Agreed Value coverage policy, or a company that will insure the trike as a unit (rare), most insurance companies will insure the original bike as it came stock from the factory. That unit now is missing the rear wheel, fender, saddlebags, much of the drive-train and other assorted parts. The original motorcycle part of the trike is now worth much less than a 2 wheeler of the same year and condition.
Everything else is an accessory - all the chrome, aftermarket seats, pin striping/graphics, foot pegs and such. Even the trike kit itself. Anything that didn't come from the factory needs to be insured under a Customization or Accessory rider. Our insurance will pay 100% of the customization added equipment up to the maximum covered. I went over the trike and documented the price of all added items with aftermarket catalogs, the trike kit (including paint and labor) and added $2000 more accessory coverage. Every insurance company is a bit different, and each state has their own rules, so YMMV. Talk to your insurance person to make sure the whole trike, including accessories, is covered.
You can see a few of the add-ons in the picture below, like the Baker wings, Ring of Fire, aftermarket windshield and a few other farkles: (Wife is not insured as an accessory)