The 200 kph is a typo. I think it should read 2000 kph - which is 1243 mph (ie ~ the 1250 mph in the article). Farther down in the article it talks about using the Lorin jet system potentially allowing a speed of 1215 mph.
Yeah. About the only thing anyone had actually achieved by the end of WWII (I think) relative to Mach 2 speeds for aircraft was firing arrow type fuselage shapes with different wing shapes in order to see how highly swept wings & deltas with different airfoil sections behaved re drag. The idea was to fire the models from cannons at different speeds and check the velocity loss over distance, using the same or similar methods as was done for for projectiles. Fire the arrow fuselage by itself and figure the drag. Then add the different wing shapes and see how they changed the velocity at a distance, vs the arrow fuselage alone. After that it is just a matter of doing the math to figure out the critical Mach values and drag curves.
Area rule had not yet been figured out (I think) so using conventional axial and centrifugal propulsion to achieve supersonic speeds was unlikely.
Yes, he was working on a supersonic ram-jet powered aircraft, the P.13a - this is where the DM-1 glider (proof of concept) stems from.
The P.13 project was actually started in 1939, but delays and other projects took priority - so no real progress in supersonic flight happened during the war.
The Me-163 had a huge problem in that the engine could propel it to beyond what the airframe could handle, even in level flight. Trying to zoom up behind enemy aircraft, like the two P-47's that were the first ever combat target of the rocket fighter, was difficult to impossible because the airplane hit compressibility, which it was not designed to handle - and nothing else was, either. The P-47's never even knew they were under attack and the Komet ran out of propellant. So they adopted the tactic of zooming up above the targets, turning off the engine, and diving on them, then zooming up above again.