I would do 4" cuttings on all of them. I root my rosemary in water. It takes at least a month to get a tiny root. I don't use rooting powder. It is just a fungicide from what an old boss told me. It doesn't help it root. I never had any luck growing lavender. I use 4" pots and keep the foliage misted daily.

I almost always use a dome like this one:

http://sgsak.com/wp-content/uploads/2014/06/propagation-dome.png

In my arid environment it would be difficult to get cuttings going with misting alone.

I never use the water method. Instead I use a seed starting mix.

If you have plants outdoors, you may also look into layering. It is another type of vegetative propagation method.

A long time poster here (who hasn't been here much in a long time) used to suggest heel cuttings for some of these herbs. If I recall correctly, she used to dip in raw honey which has a host of anti-microbial properties. I'm sure you can find her info if you search back posts. Look for "daisyduckworth."

FataMorgana

Here is a link that might be useful: Google Search: Layering

What is raw honey? Is it just honey from a bottle.

Oregano will almost certainly have rooted pieces you can just remove and plant straight away. (Self layered) No need for cuttings at all. Thyme and sage may well also have self layered and have bits ready to remove.

Rosemary will root from 6 inches pieces just stuck in the ground. Sage will root from shorter pieces stuck in a pot of cuttings mix or any free draining mix. The more sprawling varieties will also self layer.

Lavender I don't grow but I've seen two inch cuttings used.

To avoid mould I wouldn't use a bag or dome for any of these Mediterranean natives

"Raw" honey is the unpasteurized, not heated treated honey. Heat destroys the natural enzymes that provide that anti-microbial action. So Sue Bee Honey from your local supermarket won't do what you need it to. Buy from a farm stand or health food store. It is usually labeled "raw" here in the US if it is raw honey.

FataMorgana