hi sweet as sugar
everything you say sounds very normal for a bf baby. At 4 weeks old your milk supply is not fully established - your baby is still working towards doing that and by cluster feeding, particularly in the evening - she's ensuring future supply for herself. Its way too early for any kind of pattern with the feeding, its very normal for feeds to get longer and more frequent - all the demand will increase your supply so she's just doing what nature is telling her to do.
It sounds like she is getting sleepy at the breast but its tiring for her to do long, frequent feeds so she will be more half hearted in her sucks than when she was going on for 20 mins. Have you tried bf lying down, this might be away for you to get more rest.
I know this will be controversial, but i work helping women to bf and find gina ford's advice infuriating. Its aimed at bottle fed babies and its complete rubbish to talk about a breast being emptied like a bottle! A breast is never empty,obviously after a big feed theres less in it but the body is continually producing it so your baby is always getting something. Gina ford's ideas about timing bfs in the beginning are not useful - the only way to get a good milk supply is to let your baby feed as and when so dont feel pressurised by this advice.
I think once your milk is in after day 3 there isnt a lot of difference in the colour of fore and hind milk (obviously in the beginning the colostrum is yellow, but that will be long gone by now and should all appear whiter) plenty of wet and dirty nappies is all the evidence you need, sounds like you're doing a great job.
As far as expressing goes - if you can find a window to do this when your bubba is a month old you're doing well! I wouldnt put too much pressure on yourself though, you can have all on just feeding your LO. You tend to get more milk expressing while LO is feeding on the other breast, or after the first feed in the morning. But if you try and build up a freezer supply now you could be risking engorgement. Id let your body get used to what your lo needs in these first few weeks if you can - unless its very important for you to have the freezer supply now.
Hope this has been helpful, sounds like you are doing a fantastic job xx