Hi,
This combination thing is little bit "square". You can do almost all, but without additional module there is no possibility to change product package dimensions. (Yes this isn't quick, but I have done this with CSV) Also stock keeping is very stupid. You can see overall quantity, but when You need to see how many each item you have, you must look separately. For example if You sell things which only difference is length, then you can change price and weight, but not length for every combination. Other solution is sell everything separately. But for client this is pointless. Because for this item but shorter or longer he/she need search again. I hope there will be possibility when You can add/merge (whatever word) products so that every product has its own ID, but there is also possibility to group them. So You can have stock for every item and client can make choice between items without need to search again (dropdown or radiobutton, like combination at the moment). If this is possible already then someone can teach me or at least give a hint.