You will have to do more than pull out the plugs and gravity drain. To get as much oil out as possible, you will have to rotate the compressor by hand with it in a number of positions. Work dilligently and get out as much as possible.
To determine correct oil, go to aircondition.com and then click on "Straight to the Board." Post your question and they will provide an answer in short order. PAG comes in three weights, and 46 may very well be the correct one, but they will know for absolutely sure. There is a guy who will respond as "Chick." You can trust his response.