Hi, and welcome. If you are looking at gas struts, have you finished the build? If you are just starting, you don't have to consider that detail yet-just leave room for them in the galley. I did my build 3 years ago and added struts just last fall. It was easier than I thought except for cutting away part of a shelf to clear the strut. The strut sizing depends on the weight of the finished hatch. In my case, I had a full 5 feet wide hatch with inner head liner and inner lights and tail lights. I ended up with 120 pound struts to support the hatch fully open. Use McMaster-Carr for struts. Lots of options and end fittings.
Five cords of wood in, snow tires on, 5 X 8 NT frame on order. Gonna build a TD this winter.