Personal view - not a healthcare professional, only BF'd one child (to 20 months) ... "established" is one of those words that has been taken up into the lingo of a specific group of people and now serves only to divide the confident and the not.
Biologically, at 3 weeks your body probably is still getting to grips with the situation but well done and congratulations - it is fantastic that your DD is growing so strongly and I hope it continues for you. It's an excellent skill she has mastered. Feeling all gooey just thinking about lovely snuggly newborn...
Growth spurts happen at all sorts of points. you could put "# week growth spurt" into google with # = 4,5,6,7,8,9... and you'd get many many hits. In fact I just did: 4wk=1,420,000 hits, 5wk=410,000 6wk=1,170,000, 7wk 1,720,000, 8wk=375,000, 9wk=1,400,000 ........... Utterly unscientific but that's the point! every baby different.
Once you start to see a pattern in feeding times, which is in months not weeks, maybe your body will respond and you'll feel a subtle throb at 5.34pm just a second before baby starts to have a whinge - that could be one definition. Another could be when you can leave off for a few days and supply is unaffected.
Don't know about dummies/bottles, sorry. Try Kellymom.