Disenabling Cloud Sync + Lightroom Premium Questions

G'day Everyone,

I'm new to Adobe Lightroom and recently instuled what I think is the mobile version of lightroom on my new Lenovo chromebook duet. I've enjoyed editing JPEG photos on it but I plan to later edit more RAW photos as an avid wildlife and nature photographer. I heard you have to use lightroom premium in order to edit RAW files - is that true? If so, would it be compatible with my chromebook? 

Also, how would I be able to disenable automatic cloud syncing of my photos in lightroom premium? I would like to use an external hardrive to store my photos and edits on rather than the cloud.

Additonally, if I do sign up to lightroom premium for a year, the subscription apparently automatically renews which I assume means the payment would also be automatic. Is there anyway I can manualy renew and pay for another subscription?

Thank you for reading my post and I look forward to reading any\all replies.

Cheers,

Caitlin