I believe #1, #2 and #5 are Pump Piston components, #5 looks like a Wavy washer but I think its the camera flash and its really a backup.
1# Is a Seal/Wiper that Presses into the Recessed portion on top of the block where the Pump Piston is. It is essentially the same type of seal that you have in the Tank nut, Where you where asking if the orientation was correct. In both cases that should be the correct way to press them in, The bottom portion should be Open. (I can confirm if you snap a picture of the underside, but im about 99% sure that's right where you see the sizing up top) Install this AFTER you assemble the Oring/Backup into the appropriate groove.
#2 and #5 is the Pump Piston Oring and Backup, If you look at #5 it should be flat on one side and beveled to accept the oring on the Other. The Oring will fit in the pump Piston Galley inside a groove and the Backup will mate to the Oring in the same groove "ON TOP" of the Oring.
(If for some reason #5 isn't soft and pliable or doesn't match my description, don't install it in the piston galley)
#3 and #4 appear to be the Same size Oring, I suspect one is for the release (up inside where the Rod seals) and the other one maybe seals the working valve. <-- Right next to the Pump Piston.
#6 ? Well it doesn't appear to appropriate sized to backup either of the 2 orings, Maybe a seal to fit Overload Plug?
Now for the Main Ram Seal, Yes you will need to remove the snap ring. What you have is a loaded Ucup (A little surprised at that) The side with the Writing SKF 22mm USA etc will go on first and will ride against the "Flat" side of the Guide. The other end is the business, and will be outwards against the pressure.