Welll.....
Manually entering data into an array would be tedious. And, any time you need to make changes or add things... ick.
Manually creating a JSON would be even more tedious. Just making sure you got the syntax right.
Assuming you don't have a lot of experience with MySQL or PHP, what I would do is something like this. And keep in mind, this is not an ideal solution but it would be a good starting place to learn about databases.
First, I would download SQLite Studio (google it) and use it to create a database of the objects in the game. Depending on how you structured it, it would be dead easy to add levels, add new objects, etc. just by adding a new item to the table.
After you have the database I would then look at using an SQLite to JSON converter like this one: mygeodata.cloud/converter/sqlite-to-json
SQLite creates a db file that you'd upload to it. I've never used that site before so I can't promise it would work.
Then, bring your JSON into the game, parse the crap out of it and stuff all that into an array.
The advantage of that is, you could have a table for enemies, a table for asteroids and a table for drops and you could load each into separate arrays.
That being said, if you have gobs of stuff to add, arrays do have limitations.
I'm sure you could do it in firebase but, I've never worked with it so I couldn't tell you where to even start there.