Thank your friends for your attention and comments!
I've finished painting, it was not so hard – just one color. After removing masks, the only thing that was left – red roundels of national insignia and black stripes on the wings near the cockpit. Masks contains both positive and negative roundels, so I've applied them in a such way – first, I've positioned a positive roundel inside of a star (that takes some time, to do it precisely in the center):
Then, using positive roundel as a position mark, I've applied a negative mask, removing a positive mask afterwards. And it's ready for painting:
Exhausts were painted with a "chipping" color as a base for pigments. Also, I don't need to apply any decals, so I can move directly to shading and weathering now. And I like the result of using masks instead of decals, especially, when it comes to rivets and panel lines.