Here are my thoughts with 10 years of experience with our 2350.
Read through my ongoing post HERE
on things I have done over the years with our PC. Maybe some will spark an idea or two for yourself.
About keyless entry for the van doors. Back in 2007, and maybe applies today, keyless entry is a "Ford" thing and it does not come standard on their E-Series RV-model chassis. Our 2007 E350 is missing the keyless entry controller. I once researched what it would take to add one, learning that our chassis is not even wired for a keyless entry controller. I was not able to determine if the missing wire harness is something I could add myself. My point to this is, if you want keyless entry, be clear about it right up front because Phoenix may have to special order an E450 chassis with keyless entry rather than use an E450 chassis already stretched on their lot, ready for building.
We have the box awning. It is very clean looking by comparison to the motorized one, but can't compare to the ease of a push-button electric awning. I still sit on the fence over my feeling about the two types.
As I feel about our box awning, I decided to delete the rear rack and ladder. For me, that was the right decision for a very clean body as seen HERE
avoiding all the mounting holes and caulk as well as the unsightly tubing all about the rig. I actually have my rack and ladder in pieces, stored in my house basement, just in-case I ever change my mind. It has been 10 years now so I think it's time to put them up for sale on Ebay. With exception to our very first outing in 2007, I have been lucky not to need the ladder on a trip to untangle the PC from a low hanging tree branch. The rack and ladder increase entanglement anyway.
I wished we had a porch light in the rear and one on the driver side of the rig, controlled on their own shared switch. It would be very convenient to light the area all around the rig as needed. Not just when at the camp site, but also when backing into a primitive site at night. If you avoid hitting just one tree with them, they are so worth it. No tree bumps yet for us, but we got surprisingly close more than once because of darkness.
This I am not sure about, but is still worth mentioning. Phoenix might decline some of your electrical requests if you have a slide-out for it may cut off their means to channel 110V wiring along the driver side wall. Maybe they break their own unwritten code and wire 110V up and over the slide out opening.
Unless there is a parking/storage challenge with the longer 2552, I would surely get that model.....especially if getting a dinette, and even better to have a no-slide dinette so the dinette itself could be made bigger yet. The leg room, table size, and bed size would all benefit. The extra relaxing seat behind the passenger seat in the 2552 is important to have with any kind of dinette.
If your plan is to drive a lot throughout your trips as we do, ask Phoenix about the 3-way hot water tank. The 2-way heats up with propane and 110V. The 3rd method in the 3-way unit, the coolant from the Ford engine flows through the water heater, making hot water while driving. We have the 2-way water tank. I think we would have appreciated the 3-way with our travel style.
One thing I would ask Phoenix about. Can they add redundant gray and black waste tank valve control switches inside the house. Like us, your gray tank is the smaller of the two. You will find the need to blend the tanks once or twice between dumps. I am considering adding one more pair of gray & black tank valve switches so I don't have to run around outside to blend the tanks which always happens during our shower time. Needless to say it's the worst possible time to go outside and blend tanks to let the water drain out from the shower pan.
I really don't like having any more holes in our roof than necessary. (ie: roof rack & ladder). I had wondered if we could have done just as well with a Fantastic fan in the bathroom and do away with the one just outside the bathroom door. Two huge holes in the roof so close together (just a couple feet apart) doing the same job, seems redundant to me. I suppose we'd need a pass-thru grill-vent in the wall. Or maybe a bathroom door that has a gap at the top to allow air to get past a closed bathroom door.