First...congratulations on your new little girl! Hang on you're in for quite a ride...lol.
Breastmilk lasts about 5-7 days in the fridge. You can freeze it for up to 3 months. The color, taste, and smell of breastmilk will change depending upon what you eat. Don't "treat" the breastmilk before freezing it, just use a sterilized container. I use the pump and store bags made by Medela. I like them because you attach them directly to the pump, then ziplock them and put them directly into the fridge or freezer. You handle the milk a minimum number of times.
You mentioned warming up the breastmilk. If you do, DON'T use the microwave. It breaks down the breastmilk and you lose the nutritional value.
Finally...12 weeks seems awfully early for a sippy cup, straw, and cereal. I don't think I even introduced my son to a bottle until he was about 3 1/2 months old. My pedi didn't want him on solid foods until he was 6 months old. She had me introduce the sippy cup at 9 months. (He's now 10 months old.) I'd recommend talking with your Pedi before taking any of these steps. I'd also keep trying the bottle. A couple of suggestions...have you tried a different nipple/bottle? Also, have your husband give the bottle to your daughter. You shouldn't be anywhere near; you may even need to leave the house. (I had to go into the back bedroom and close the door.) If she smells you, she won't want to take the bottle. It will take a bit of trying. Once she's easily taking the bottle from your husband, then you can try giving it to her. Good luck!