Hi Deck,
Thats all going to depend on your use...or abuse.
I change the oil quite often. About every 10 hours or if I see a pressure drop that doesn't come back.
Change the filter in between oil changes, and with every oil change.
Grease the U-joints and thrust bearing every time you go out or come back, along with your bearing buddies.
Top off the oil in your bowl after every trip.
Personally I probably change my 455 oil a little too much, but I feel better that way. As soon as it begins to change color, it gets one more weekend and I suck out 9 quarts and pump in 9 more.
For oil I usually use Valvoline VR1 50 wt when the water warms up. And I use a remote filter, so I use AC Delco PF2 I believe. Use any filter OTHER THAN A FRAM!!!!