Starting reta, need help/ advice

Hey guys, so i’m starting reta next week as i’ve just ordered my first vial and was just wondering if anyone could give me some advice and answer some questions I have. :) Just quickly I do want to mention that I have researched and am continuing to but I guess everyone is different which is why i can’t find definitive answers, also I don’t care if anyone claims I “shouldn’t use it if I don’t know what I’m doing” because we all start somewhere so pls be nice.
Firstly, what dose should I start with? Some people start with 0.5 and have bad side effects but some start with 1mg and are completely fine so I’m a little stuck there.
Secondly, I’ve seen people mention bac water? What is it? And is it something compulsory or not?
Lastly, where does everyone find injecting it is best? Majority I’ve seen use the lower stomach so wondering if that’s the safest/ only place.
That’s all for now, if I have new questions or concerns I’ll edit and add to the post. Thanks for any help!