Kevin,
Back to some of your questions.
Over 1,200,000 P.38s were made by the Germans during WWII. It was considered the most innovative handgun design of the War. Our current U.S. M9 Beretta uses the same locking block system (with a proof magnafluxed slide).
The P.38 was not an 'Officers' sidearm exclusively.
The vast majority in fact were issued to all branches of the German Army for use by motorcycle dispatch riders, machine gun crews, MPs, NCOs, as well as officers of the line.
The 42 'j' block P.38s were made in November of 1942. Serials ran well into the 'k' block that year. Walther started fresh every year with 10,000 no letter series -called NLS - then 10,000 'a' block and so on. Estimated 120,000 in 1942.
Reading the right slide left to right, you have an 'eagle/359' which is the army acceptance for the completed slide assembly.
The center eagle clutching the swastica is the firing proof with test high pressure ammo. You will also see this proof on both the barrel lug with the slide retracted and on the locking block (which should have the last three digits and letter suffix of the same serial number on the gun.
The e/359 to the right is the army acceptance stamp of the completed pistol.
The grips are made of Bakelite rather than plastic and one should use care in banging them around.
The correct magazine for it is marked with a 'P.38' (no letter 'v') on the left side and a right side up e/359 on the rear spine.
The loop was for a lanyard that kept the soldier from losing the pistol.
The use of lanyards date to horse cavalry when a trooper needed to be able to drop the pistol to control the horse when wielding both the pistol and saber.
Lanyard use was relatively obsolete by WWII and as a result, P.38 lanyards are considered rare.
Shooting.
If it were mine, I would buy some of the Winchester 'white box' and enjoy it once and a while. These are old guns and like mentioned some slides have been known to crack at the forward left side of the top opening.
The rear sight is NOT adjustable. It holds the firing pin cover down and also retains the safety and hammer drop parts. So don't try to tap it for windage adjustments. That is why the front sight is moveable.
Also, DO NOT use the safety to drop the hammer! The firing pin on the P.38 was a weak point and could be crystallized to the point that the gun could fire when you let the hammer drop. Post war P.38 manufacture addressed this with a new design firing pin.
I would most strongly recommend that you not use this feature as it sounds like you are new to the gun and its design. Just unload it instead.
Value.
Again as mentioned, condition is everything. Without pictures, one can only guess at what slight pitting means. Get to a camera.
JT