The sub looks amazing! As for decals, you could just say that the sub was undergoing sea trials and hadn't been assigned to a kriegsmarine unit yet, since going off of what I recall of my visit to U-505 years ago, the only real unique markings would be the hull number and the emblem on the tower, both of which I figure wouldn't be too hard to add down the line.
As for me, I'll add pics of the latest model I've made: a Tamiya 1/48 Howitzer Motor Carriage, a.k.a. the "M8 Scott" done with decals for the 106th Cavalry Reconnaissance Group as deployed in Germany in Feb. 1945.
I haven't been making tanks long (only built one other which also makes a guest appearance later) but even with two under my belt, I'm stunned to see how much of the exterior of these things are used as storage for tools and can really contrast with the base color of the tank. The way it was done here on the Scott is also odd - half of these tools were separately cast while the other half are actually cast directly on the hull itself. All the wood on the tools should be the same color, but what happened is the original color I used I decided looked better as the leather straps on the canvas, so I meant to repaint all the wood. I don't mind, though, I think the shovel being a different color gives a little character as it looks like they had to replace the tool at some point.
The steel cable is an interesting detail on the kit, totally optional, but it's a black string you have to cut to length (the full length included is over twice the necessary amount) and glue the ends into the hooks, which you then have to thread the tie-rings through and then attach. You also need to paint the entire cable which was really awkward. Worse still, even fully painted, the string doesn't like to 'hug' the hull contours like it would on the prototype since these would be heavy cables, but I'm cheating a little here by stuffing a bit of the string under the turret itself which keeps it sitting pretty and proper.
What's cool about this kit is that not only does the turret move (the canvas roll on the back barely clears the antenna mount but just enough that it'll never hit) but the cannon itself can move up and down, while at the same time you can look from above straight through the turret to the vehicle's floor panels. The metal weights that give the model some heft are hidden just forward but you'll never see them.

And here's the M8 with the aforementioned first 'tank' I ever built; a Tamiya 1/48 Panzer IV Wirbelwind (still need to track down what happened to its small gun, hence why there's an unpainted piece of scrap brass wire shoved in it). The M8 came with its own little commander figure but I haven't painted him yet, so here the commander from the Wirbelwind stands in to provide a sense of what a tiny little box the M8 is compared to a mainstay WWII tank chassis.