I’m studying Japanese, so I know how tricky kanji is!
My advice is to practice writing the kanji BIG first. You don’t need to worry about stroke order if you’re just writing an address and want it to look right. There is a logic to stroke order (in Japanese it’s left to right, top to bottom, in Chinese language characters it’s different)
Start by downloading a Chinese dictionary app onto your phone so you can copy and paste the address into the dictionary on your phone. Most dictionary apps for Chinese/Japanese will show you how to write the characters line-by-line, so you can recreate it bit by bit until it’s finished.
Write them one at a time. Practice writing the character BIG on some scrap paper and then you can write it on the postcard. Do them one at a time, there’s no rush.