Questions

re: Iphone : Can i enable the icloud photos without downloading all my icloud photos on my mobile device? e.g all photos taken from my phone to be uploaded to icloud photos without downloading all the icloud photos in the library and waste device space

No. iCloud Photos is a syncing service. All photos are synced with iCloud and all other devices connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: https://support.apple.com/en-us/HT204264

re: I enabled photo stream on my iphone without enabling icloud photos. Icloud photos on mu Mac is ebables however i cannot see the My photo stream on Photos app

See the following from My Photo Stream - Apple Support

If you use another device with the same Apple ID that has only My Photo Stream turned on, photos that you take on that device upload only to My Photo Stream. They don't appear on any devices that have only iCloud Photos enabled.