Hi, again
As I stated earlier — your app needs to be refactored to become maintainable and implement those features you described
As here is limited proposal input, will describe only one question, other will follow in chat.
How many emails / SMS will be possible in the single upload? — depends on server configuration, as you described if using utf-8 one SMS will take about 512 bytes - 1 kb, so 1 000-2 000 in 1 mb. So if you set upload max to 100 mb — 100 000 - 200 000. Then as it contains text it is highly compressible, so you can expect about 2x compression ratio and it will be up to 400 000 in 100 mb