I'm in the middle of building this Lepin kit too, using the official LEGO instructions (available from Lego.com) rather than the Lepin version, and I have had some of the same problems you have, but in some cases there are solutions in the box. Firstly, those 2x1 light bley hinge tops that are missing - use black ones, and save the 2x2 hinge tops for the dark bley tiles that hinge down in the gap on the central piece between the mandlbles - in your picture above, you can see the six tiles in question in their upright position - they should actually be angled down to a sympathetic angle to the slopes either side of them. Secondly, the axle connectors for the landing gear. In my kit, Lepin supplied both the ridged connectors, which have the friction problem you describe, and also some different axle connectors that are smooth, but fit right down between the studs on the landing gear, so they have a much more secure connection. The instructions don't use them anywhere else, so I can only assume that is what they are there for. In general, building this thing has been a good experience, but I've found that Lepin Technic pins are much more brittle than real LEGO ones, and also quite a bit more difficult to fit into holes. The regular system bricks also seem to be of a more easily scratched plastic than LEGO, as several of my pieces came out of the box with minor gouges. Anyway, I hope these piece suggestions help.