Reducing Bulk on a touring trip
'Bulk' is mostly about whether all of your luggage will fit in your bags. ie is the volume of your luggage less than the capacity of your bags. So it depends on how much stuff you want to take, and how big your panniers are.

Aerodynamics doesn't really matter for touring. Unless you are cycling rather fast, or it is very windy. Usually the weight of your bike and luggage will make more difference to your speed and effort required.

For reducing bulk, the main thing is taking less stuff. It also depends on how you pack it. eg if clothes are folded properly, they will be less bulky. Some things can be squashed smaller, eg sleeping bags. Compression bags can help with this.

It is worth leaving some spare space in your bags. You may want to buy things along the way. eg food supplies can be surprisingly bulky. Or any essential gear you find is missing, or any souvenirs you want to take home. Also after packing and unpacking a few times, you will probably find things don't fit as neatly, so end up taking more space.

Its up to you how you much you want to carry. Carrying lots of stuff will slow you down a bit while cycling, so you won't cover as much distance. And it may affect the handling of the bike, so its not as fun to ride. On the other hand, it is nice to be comfortable while camping, and have all of the kit you might want.