Yes this will fit an M5E1 Upper
You can put the M-Lock anywhere on the rail as long as it on the 12,3,6, or 9 positioning.
The 15.5" ODIN Works AR Rune Forend weighs 6.55 oz, with the included barrel nut and included picatinny sight rail, it weighs 10.4 oz.
The manufacturer doesn't state how many M-LOK slots are on the 6 o'clock position of the ODIN Works AR Rune Forend but the 3 and 9 o'clock position has 4 M-LOK slots.
The ODIN Works AR Rune Forend has an inside diameter of 1.47"x1.63".
Yes, the inside dimensions are 1.47x1.63"
Yes, it comes with the forend adapter and barrel nut that are shown in photo #5.
This will be compatible with your 16 inch barrel.
The dimensions inside are 1.47" x 1.63"
Yes this installs on a bar nut receiver