Regarding your question about weight differences between a Quantum shell and the other materials offered by Nunatak, there's a weight estimate provided in the chart at the following page of the Nunatak website showing information about various shell options -- including total weight for a quilt with each shell option for each size:
From the chart at the above page, it appears as a general matter that a quilt using a quantum shell weighs about one ounce less than a quilt with microlight shell, which in turn weighs about two ounces less than one with Epic shell.
Also helpful is the following link at the above page that takes you to a description of characteristics of fabrics used by Nunatak, and identifying some of the trade-offs inherit in each material (weight, durability, etc.):
At the time I ordered my Arc Alpinist, I had hoped to have it in time for a fall backpacking trip that I had already planned to the Enchantments. Since there was simply no way that the quilt would be completed in time, Tom kindly sent me a demo Arc Alpinist with Epic shell for me to use on my trip. I much appreciated the Epic-shelled loaner, and not just because I had a trip planned. The loaner quilt gave me the chance to experience Epic's "loftiness" and breathability. It was excellent on both counts.
I also appreciated Epic's durability since I for sure wanted to return the loaner in fine shape. At that price, I couldn't afford more than one quilt and looked forward to having the custom version that I ordered!
Tom is of course the best source for information on the Arc Alpinist. From what I've heard and from my personal experience a few years ago, he is extremely helpful (and also extremely patient) in discussing a potential order. He has no doubt by now heard just about every question that might be imagined, which probably helps explain why his website is full of a lot of great information.
With a custom-made quilt that's so expensive, it is very reassuring to discuss options with Tom to be certain that features you "believe" you want to include in the order will in fact meet your needs and expectations.
As for straps, my quilt has the standard number (two) and I've had no particular difficulty using them if there's a need for some extra warmth. It's easy (for me, anyway) to reach under my legs, fasten the lower strap, then reach behind my back to fasten the upper strap. All of this is done while the quilt is loosely drapped over me.
I don't try to fasten the straps around my pad. Doesn't seem necessary for comfort -- at least not so far.
There's an additional feature for securing the head of the quilt if needed to seal the interior for warmth. A snap connects the quilt's two corners at that end, and you can secure the corners by reaching behind your head and snapping the corners together behind your neck. There's an elastic cord sewn into the hem at that end so that the entire end can be snugged up with a cordlock once the two corners are fastened. Simple and quick.