You use the word "routine" and I think that's the right word. You can start to lay the groundwork for a routine but I truly think it's easiest to let your baby lead the way. If your baby is only 4 weeks then you should give yourself *at least* 2 more months before worrying about a routine. They change so much and so fast!
As for your snacker, mine has been that way since week 3 and I quickly learned I can't change him. He eats for 3-5 minutes and then is DONE, no matter how much I try to get him to eat more. Why fight? Why make him cry more than he already is going to? As long as your baby is gaining weight she's getting enough milk. Here how I look at it. My baby nurses for 5 minutes every two hours, including at night so that's 12 feedings and a total of 60 minutes I spend nursing each day. I have a friend who feeds her daughter every 3 hours and nurses for 15-20 minutes. So that's 120-160 minutes worth of nursing assuming it's about 8 feedings. I'd much rather nurse only 1 hour per day than 2 or more!!! Sometimes these "snacks" are a "full feeding" if your baby is very efficient at getting the milk out. Good luck!