Hiya ladies
Just thought I'd pop in my tuppence worth as we started EASY DD2 (Callie) right away
I think the most important thing at the moment is that you concentrate on getting the activities in the right order, so Eat then some Activity then Sleep. Then of course, You time - or You and older LO time
The timings don't really matter at the moment, most babies don't get onto a good predictable EASY until nearer 6/8 weeks although I think it was about 10 weeks before things were consistent for us. I really wouldn't focus too much on the 3 hourly feeding at the moment. It will come with time but is often 'messed up' at this age by short naps etc.
At 3 weeks your LO's will only be able to be up for about 1 hour at a time, and this will include feeding, changing, cuddles, wind down. If you are having nice long naps that is fantastic. At this age they should be sleeping 1-2 hours out of every 3.
Now is a good time to begin establishing good nap time and bedtime routines, so that your babies get used to that routine and come to anticipate what is happening next in their day.
As for sleep training, it is up to you when you begin. We found that Callie 'woke up' around 5 weeks or so and getting her to settle became a bit more difficult then. That is when we began to use pat/shh for naps and work on independent sleep.
HTH. Enjoy those tiny babies!