Search on here for my name & radio. The adapter can be had for under $10. That adapter is all you need to add a $50-150 radio. Speakers & antenna are already there. No need to pop the roof to install it either, just remove the plate over the radio hole.
I got the big alternator required for the rear defroster (new window with the heater elements in it). I like it for the snow. Front & rear wipers are handy.
Air ride seat is an extra Grand. But if you have a bad back like me so worth it.
Loaded rear tires aren't mandatory like they were on my old
L3200. That machine was way lighter, especially in the back. Good idea to load the rears for traction & stability, but it won't help the low HP.
I got 3 rear remotes, 2 float, 1 double acting detent. Ordered TnT, but the (non-Kubita) cylinders the dealer kept getting sucked. Refunded & im waiting on FitRite cylinders still.
Don't get the rear work lights. I put in my own front & rear light bars. You'll be better off getting your own LED lights to replace the standard front ones & add the rears. Rears are all wired up, just need to plug into the wires there & plug in a new rear switch. I put in overkill power to run my light bars & other future stuff. But the stick wiring will handle some slightly bigger than stock lights.
Tires are a personal or task choice. R1s have better traction, especially in loose dirt & mud. R4s are more durable, last longer, tear up turf less & cary heavier loads a little better. I'm happy with my compromise R4s.