If wood flooring( going right on top of wood sub floor.. which are floor boards) is over 4" wide does it get glued down? Glued and nailed or just nailed? Thanks

BTW should I put plywood over the sub floors planks?

You should be able to attach new flooring directly to the sub-floor. There is a building code that sub-floor was installed so it supports a certain amount of weight. Check to make sure that it has been fastened well. Adding more plywood can be done. I would recommend using sub-floor adhesive along with fasteners if you add a layer.
Glueing is recommended for flooring that is 5 inch width and wider. I have never used glue for solid wood in my area. You need to know the moisture content of the wood that works for your area. The T&G will support the flooring if one of the fasteners doesn't hit a sub-floor plank but misses into the gap between sub-floor planks. You could double the number of fasteners to every 6 inches if you would like to be sure that the flooring is held adequately.

thank you