Glass has poor thermal properties, so when a temperature change occurs, moisture may condense inside the frame and soak into the art paper. That is why photographs and other images sometimes stick to the glass. Also, condensed moisture is a contributor to mold and mildew inside frames.
Instead of Museum Glass, you could use Museum Optium Acrylic, which has exactly the same optical properties, but half the weight, 20 times the shatter resistance, and much better thermal properties. Also, unlike standard acrylic sheets, it has no static charge.
On the back, you could use standard acrylic or, if light exposure is anticipated, use UV-filtering acrylic.
Another consideration in overlay/direct contact mounting is the possibility of mechanical damage to the art from the glazing in contact, such as abrasion. If the art paper's surface is smooth (not textured) and durable (not friable), then there probably would be no problems with the framing design.