50 Gb iCloud storage is an awful lot, and it would hold this much:
Around 25,000 high-resolution photos or about 10 hours of high resolution video. It would cost 99 cents a month, that's a little short of $12 a year. Do you seriously have that much on your phone?
Where mail is concerned, I can only suggest that you don't store too much. A lot of the mail I receive is unsolicited and mainly from USA sources. I'm British, so they all get unsubscribed. Some don't even have an unsubscribe facility, in which they get deleted, so keep an eye on your mail storage. If it gets into even the low gigabyte range, you need to get rid of at least any unsolicited mail.