Lots of questions in there. Here comes a wall of text in response.
The 156R vs 156D debate for a Grand boat has a pretty clear choice for me. The 156R is definitely larger then the 156D and will definitely more happily carry a bunch of gear. I know a few guys who use the R as their Grand boat and it seems to do very well. If you look at the wireframe drawings for both boats, the D starts to taper much sooner plus it has continuous rocker so the depth goes away sooner as well. This will make a bit faster and quicker to turn, but it will also draft more when you load it up a bunch. There is a significant amount less room inside because of this, so you might find yourself having a higher gear pile. The R, with its flat bottom and big tubes all around is, like you said, great for hauling gear without getting bogged down. I think the main reason you would go with the D over the R is if you planned to paddle raft with a crew of people more and use it a few times a year as a multi-day oar rig. If you are just hauling gear the R is definitely better suited IMHO. Keep reading though.
I have a 136DD as my small/medium boat, and while it may not be as deep, it actually has about the same floor space as the 156R (as directly compared during a trip with a friend over the summer that has a 156R). That said, just because there is room doesn't mean there is weight capacity and its very easy to overload that boat and it gets really sluggish and hard to maneuver when you do. The hull is really flat and the rocker happens in the last 18" of the boat, so I think it can be a bit like a battering ram and can stall in big waves. As long as you don't go crazy overloading it and you aren't expected to carry a passenger or a as much gear as the 16' boats, I think it would do fine in the Grand. I have a trip in May 2018 and I'm planning on taking it even though I have a 16' Avon that would probably take care of me and haul more gear...but that is mostly because I want a more exciting ride. I did 2 Westwater, 2 Main Salmon trips, and 2 lodore trips in it this year (with one Lodore trip being an 8 day trip starting at Flaming Gorge dam) in the 136DD and it did a great job and its certainly not going anywhere soon. I will say that if the 126DD that just went up on the website was available when I got the 136DD, I think I would have had a hard choice between them. The one thing I would change about the 136DD is to have the rocker more like the 126DD and 160DD i.e. a bit less abrubt and a bit longer. I think it would be a bit faster and would punch holes a bit better. For more thoughts, you can read my review in this thread... https://www.mountainbuzz.com/forums/f...tml#post617522
If I ever replace my 16' Avon Pro, the 160DD is at the top of the list. Floor space is massive, the diminished tubes really help with wave punching and minimizing the profile in the wind. I've only seen a few on the river, but the people who have them seem very happy with them. It is obviously a bit longer then the 156R, but its about the same width. The tubes are smaller, and the diminished tubes makes for, as I said already, a massive amount of interior floor space. This is my favorite thing about the 136DD, and I can only imagine what it would be like the with the 160DD. My Avon is still doing great and since I got the 136DD I haven't actually taken it out so I don't see a need anytime soon, but I do salivate over the 160DD sometimes. Maravia makes a similar boat as well but I think I prefer the Aire for various reasons (warranty and materials) but they are both good boats.
I do have a trailer, but I also got my Avon before I had it so I understand your concerns. Honestly, from a transport and ease of setup standpoint, the 156R and 160DD aren't gonna make a huge difference. They are only 4 pounds difference, and I bet they basically roll up to about the same size. The frame is about the same size too, since they are basically the same width and length. If it were me, for those reasons, I wouldn't hesitate to get the 160DD given the choice between both of the three boats you listed but its down to person preference and I'm sure you would be happy with whichever one you get.
Oh, and as far as rolling Aire rafts up...I've had a good summer and my 136DD has been rolled up in the back of my truck for most of the summer (at least when it hasn't been used...which is a lot) since I picked it up. I used my trailer a bit with it, but ended up needing it for other stuff so I've been rigging and de-rigging when I use it. I also did a few trips like the first Main Salmon trip where we did a Jet boat shuttle and I would have had to de-rig the boat anyways so I just drove without the trailer.
Its certainly no Hypalon boat that rolls up easy (my 16' Avon rolls about the same size or smaller then the 136), but it also has done just fine being rolled up. Aires aren't like Maravias where they don't deal with being rolled up for long periods of time, so I wouldn't hesitate to get one if you can't swing a trailer. Having a trailer certainly makes it more convenient, but logistically it can be a challenge for sure. At least for me though, I wouldn't hesistate to get any of the boats based on having to roll them up or not.
Oh, and while you could certainly have no problem using a 5x8 enclosed trailer for transporting stuff broken down, its definitely not gonna take an inflated raft or even a frame for a 15-16' boat when its setup. I know the frame for my Avon doesn't fit easily in a trailer that size.
p.s. I have some friends who are friends with the Aire crew, and there are rumours about a 148DD coming out. Its far from definite, but might be a good compromise for ya if you can wait. Might be worth calling and asking them about it. If its anything like the 136DD, you'll have the same amount of room as a boat two feet longer. If it comes out and it is what I imagine, part of me would be majorly tempted to sell both my current rafts and get a 126DD (or a sport cat) and a 148DD.