I suggest reading Gael’s Post about this topic: Some clarification regarding security vs privacy in /e/OS
If you really care about security because you are a person with a threat - don’t use /e/OS. Use graphene instead.
If you care about mass-survaliance without a threat - it’s probably fine to use /e/OS. In the end, its Android with some changes to remove most google Services.
Also something to consider is which phone do you have or want. Graphene likes to present itself like the best option, and in some ways it is, but the hardware is extremely limited. This is an aspect to consider.
About the cloud: I used it but switched to Proton as it seems more reliable. Although this experience is now a year old, so take it with a grain of salt.