You are not over ambitious, making baby food is super easy. I bought the magic bullet from Bed, Bath and Beyond (used my 20% coupon) and voila, it was that easy! I bought these baby food cubes from One Step Ahead (google it). I also got the book, Super Baby Food which talks you through each stage, step by step process which foods are safe to introduce at what months, etc. The first safe foods are rice cereal, avocado (great fat for the brain) bananas, and organic sweet potatoes. When buying fresh or frozen produce, you want to buy the organic whenever you can, especially for the dirty dozen list. Go to www.ewg.org for that list. It is a list of the 12 fruits and veggies that contain the highest level of pesticide residue. Oats is not a safe food especially at 4m b/c it can cause allergies to gluten later in life, you typically wait until 7-8m for that one.
However...4m is still very early to be introducing foods, anything before 6m will make them likely to develop food intolerances or food allergies. And is she sitting up on her own? I noticed someone else brought that up. So just b/c she is of the "safe" age, she may not by physically ready either. Putting the cereal in the bottle is not recommended either, it will expand their stomachs and cause over-feeding.
Another great book called Mother Daughter Wisdom by Dr. Christine Northrup is wonderful and discusses this in her book. (It is a book you'll have through life, it talks about each life stage through the age of 21yrs, it is beautfully written and Oprah's favorite OB/GYN).
I always bought some jarred food by Earth Organics or O Organics first to introduce the foods before I made them, you have to be careful of the seeded fruits like rasberries, strawberries, b/c baby food companies take out the seeds, if you buy frozen and puree them, the seeds is what causes the allergies.
It is a lot of fun, well worth the time investment and you'll save about $300-$400 per year by making your own baby food.
Let me know if you have questions, I specialize in Mother and Children health and wellness.
J. W. MPH
Wellness Educator/Lifestyle and Wellness Consultant