Regarding the sausage, I'd brown it first, cut or uncut and then let it cook in the sauce. Browning is where all the meaty flavor comes from.
Also, sage and oregano taste totaly different and are not interchangeable, IMO. Definitely go with oregano in an italian-type tomato sauce. Marjoram and oregano are related and more interchangeable.
Less is not more. More is more and more is fabulous.