Oil pressure should be up in a couple of seconds. I don't think it is the filter (unless it is damaged) causing such a problem. It could be the sender but by hearing the valvetrain noises, it sounds like a serious problem. It could be one of the oil tubes or tired oil pump. Once you start the engine, does it just stay at 0 or does it move and then fall. For sure, take it for a checkup and don't drive it too much.