How many times should one say, "Subhan Allah 'adada ma khalaqa..." (Glory be to Allah as many times as the number of His creations...) and "Alhamdulillah 'adada ma khalaqa..." (Praise be to Allah as many times as the number of His creations...) to attain the virtue of this remembrance?

The hadith is authentic, and it is hoped that the stated reward will be attained by whoever recites it once. Al-Shawkani mentioned that the remembrance (dhikr) multiplies and increases in number according to what the reciter referred to, even if the remembrance itself is not repeated. It is good to recite this dhikr frequently without adhering to a specific number, because the Sharia encouraged frequent remembrance in general, as Allah Almighty says: "O you who have believed, remember Allah with much remembrance" (Quran 33:41), and as the Prophet (peace be upon him) said: "The Mufarridun have gone ahead." They said: "Who are the Mufarridun, O Messenger of Allah?" He said: "Those men and women who remember Allah much."