Welcome to the GSG 1911 club. I've put 3408 rounds (according to my log) through my Sig 1911 (same pistol) and I concur that's it a fun gun to shoot.
View of the business end (some weird scratching on the guide rod plug after the first day of firing - from rubbing on the barrel bushing? - zoom in
here)
One of the unfortunate things about this pistol is that it suffers a lot of cosmetic wear. What you're seeing is normal.
Disassembled, and my $0.05 snap cap lol - I did, before first use of the gun, lightly sand the rails on the frame with 400 grit sandpaper until the paint was just removed, to speed up the wearing in process, and I think it helped - again, more on this below
Good idea on sanding the rails. You can also stand to do the same sanding/polishing on the inside of the slide where it makes contact with the rails, and where the barrel makes contact with the slide. I'll take pics later but basically my slide is completely sanded on the inside.
Also, my two times cleaning the gun after the range (and of course I cleaned the gun before first use), I noticed some gritty stuff and tiny shiny metal flakes around the slide and rails on the frame, no doubt a part of the wearing in process? Or at least I hope it's normal and it'll go away soon. It's a little disappointing too, how quickly the slide-stop notch gets dinged up - I understand it's normal for this gun and the slide should last a long time, but the way it's wearing away right now doesn't fill me with confidence. Otherwise, I'm really enjoying the GSG 1911.
I've already stated my round count and mine is still running solid. The gritty/shiny stuff is again part of the wearing in process. It may take longer for that to go away than you like. Just keep shooting it. I figure I put 1000 rounds through mine until I finally stopped seeing the wear. I find this pistol (other than the cosmetic wear) has two problems. Hopefully you don't have any issues, but if you do, I hope this helps.
Feed Issues
Clean your magazines. It won't take long until you start seeing some feed issues, particularly with the second round. Sometimes the spring doesn't push up on the follower enough and the slide doesn't strip the next round off. This could lead to you firing on an empty chamber which is generally frowned upon with rimfire. In addition, make sure that the magazine springs, when uncompressed, are sitting at least at 6 inches in length. I've found that also has an effect on feeding. If you notice your springs are shorter than this length, just give them a stretch.
If I remember correctly, GSG recommends the use of CCI Mini-Mags. I've never had a feed issue with these, even before all the polishing and wearing in. They just pack enough oomph to get that slide to cycle fully every time. After polishing and wearing in, the only round that have failed to go bang and cycle properly are Winchester bulk 36gr. I'm thinking that's more a commentary on the round rather than the pistol.
Light primer strikes
Also, look for a video on YouTube on how to clean the firing pin channel on this pistol. If you press the trigger, it goes click and nothing happens, chances are that the firing pin is gummed up due to a buildup of powder. My first reaction with this pistol is that if this happens, I immediately #### the hammer and fire again. I'd say 49/50 times the round goes bang doing this. If this doesn't cause the round to go off, I wait a minute in case it's a hangfire and then check for an empty chamber. Some will argue that I should wait a minute for the hangfire and then press check instead of immediately cocking and firing to prevent dry fire.
Based on the history of my pistol and how it has performed over the last 2000 rounds, the stats are in favour of a light primer strike rather than an empty chamber. YMMV. Err on the side of safety first and make your own decision later.
If you can find the CCI Blazer rounds, they're solid. Something that is also worth a look is Federal AutoMatch.
Finally, if you plan on using this pistol for something like Steel Challenge or other action shooting, you may want to consider removing the magazine disconnector. Plenty of footage on YouTube on how to do this. The reason for this is because a number of ranges want the hammer down between stages. So, you'd have to either empty your mag or keep an empty one handy, put it back in to the pistol and then slowly release the hammer so you don't dry fire on an empty chamber. In removing the disconnector, I just have to eject the magazine and ease the hammer down.