Formula Question

Hi... after 8 months of breast feeding and the last several weeks of pumping, I am ready to transition to formula for the last 1.5-2 months. My supply is dropping and I’m preparing to go back to work.

I have never used formula before and I have some dumb questions that I was hoping you ladies can help me with!

I bought the ready to use kind since I’ll be mixing it with breastmilk while we transition. After the transition - is powder or liquid easier?

Can I heat breastmilk and formula together in bottle warmer?

If going out, I know the powder can be mixed at room temperature. What about ready made? I saw it must be used within 48 hours and refrigerated. Can I put a bottle in cooler and it be ok??

Sorry I just feel overwhelmed by this and feel silly asking these questions.