Help plz...

S • First time mom
Hi everyone... I'm a first time mom... 
Can all mothers tell me how they prepare formula for their babies plz... The entire stock of milk for a day or one feed at a time???
Also if you prepare milk for a day how do you warm it...
My baby takes something between 2.5 oz per feed so how to prepare formula for such babies... Also my baby is very gassy so I have to be very careful of my measurements....
Your help n suggestions would be appreciated....