I wouldn't put microfibre as the very inside layer that goes on bubbas toosh only because it sucks the moisture out and will dry their skin out really really badly. The microfibre underneath the velour or other bamboo layer will owrk fine. you don't NEED to have that syntethic wicking layer...it is only there to keep baby's bum feeling a bit more dry. If you have an average wetter and change your nappies often enough the synthetic layer is not essential.....when I make Connor's nappies the only synthetic I use is the minky and PUL on the outside...everything else is bamboo.

With sewing the elastic on I tend to put it on through the inside layer(s) only so maximum of two layers...you should try not to sew elastic onto the PUL or outside layers as this will cause wicking thorugh the stitching to the outside. You should also be able to adjust the pressure of your machine foot if you are having troubles getting through a thick layer and using a needle for heavy fabrics such as a stretch ballpoint or denim needle can help also.