Geo I am impressed with you. Let me welcome you to the forum.
I would listen to Kalle. He has this under control.
I will add this we are use to 24 bit recording because its far easier to get good quality recordings with 24 bits than it is with 16 bits. But one can get outstanding recordings recording 16 bits. One big reason is 24 bits is quieter. With 16 bits the recordest has to be very careful about his levels. To high and you get digital clipping to low and you get a lot of noise. With 24 bits one can be lazy and still get usable recordings.
We think of Sonar as a pro level program that is meant to use gear that has a bit of polish to it. That does not mean that yours wont work it means it could be more trouble than it is worth.
A good solid audio interface should prove to be not that expensive yet offer quality performance. It will also mean good drivers and little trouble in setup.
Because you don't seem to need at present a multi channel card one that offers 2 channels would not break the bank and serve you well.
Don't worry about specs at present most cards that we would recommend will be more than adequate.
Ask here what others have found to work and you will get good answers.
You patience in responding is impressive.
We are here to help with any questions you have.