I'm a fairly "round" guy and I find there's enough room in the pilot house for me, although I don't find the seating all that "comfy" for the driver. I usually sit on the port side so I don't need to keep flipping the seat out of the way to exit the pilothouse. I'm probably going to go with a pair of 30" tall, folding ,padded, barstools. I'm short and find the stock seat is too far from the wheel and the foot rest is too low. I can "scootch" a barstool forward so my stubby arms can reach the wheel more comfortably. As a general habit, I usually drive standing up (a habit I've had in most boats for years). On long stretches I use the autopilot so I can sit where I want. I've never missed a backrest, but again, That's probably just me. Maybe someday I'll move the wheel off centre to port, and relocate the shifter to port as well so the driver doesn't block the door when in position (might be easier to change the door to the portside?)
I've looked at making a zip-on curtain for the end of the boomtent and it's definitely do-able. The boom comes closer to the end of the boat than it looks in most pictures (mine ends about 15 inches from the rail). Unless the sun is behind you there's decent shade. I'm sure there's alot of variation when it comes to boom length and mast height as well. I'm also planning on installing "lee cloths" on the rails to reduce the reflected glare.
The cabin is well ventilated (are there supposed to be screens for the side windows??)