There is a little test you can do to check the weld ability of the material.
Take a 1"x2"x1/4" C/S tab and fillet weld it an area you intend to repair and filet weld one side with the welding rod you plan to use. After it cools try to knock it off from the welded side. If breaks out the base metal you will have change welding procedures.
I would use any good repair/service rod, we used AllState 275 (actually 312 S/S) otherwise use a new box of 7018 rods. For build up use the 7018.
Make sure you welding ground as close as possible the area of the welding to avoid going through a bearing.
You didn't say, are any of these welds going to carry high loads?
What is your location?