Congratulations on starting reloading. It is good to be careful. You are measuring more than many/most. That can be good.
#1 - This Rem primer thing is interesting. I have no experience with them. IME, there are 2 things not being considered here. First, primers can and do compress slightly during reloading. That is because the anvil must be solidly set to the base of the primer pocket. Also, the cup can be squished slightly when seating. That said, if a properly uniformed primer pocket which you have measured, won't take the primer, I would call Remington and ask for help.
#2 I know you want to trim, but in general, trimming 45 ACP is a complete waste of time. I just passed ~100 45 ACP cases through a caliper set to 0.888" I feel safe!
Regarding sizing, I believe SAAMI is a group which makes chamber drawings( and apparently cartridge dwgs). Cases need to be undersized to the chamber. Each die maker is making dies which should make brass cases fit and provide reasonable accuracy.
#3 45 Colt has been around so long, it has changed specification several times. Heck, .456 is probably from some run of 1890 Colt's! Modern 45 Colts are made to fire 45 Colt ammo with a groove dia of about 0.450 - 0.451. The throat needs to be groove dia or larger. In general, Ruger's are about .451" groove with ideally .4525" throats. All this says is .452" cast or .451" jacketed bullets will most likely provide good accuracy. .450" bullets should be returned as defective because even a groove dia of .450 would rather see .451 or .452 bullets.
Remember, SAAMI is an association. From there, manufacturers are making chambers and ammo based on their own real tolerances, tool wear allowance, etc. I can see a few errors in the 45 Colt chamber dwg based on my own experience. On the other hand, my 45 Colt is fairly accurate. If Ruger went away from SAAMI to make it bettter, I guess better for me!