Your mission is to keep that oven at 250 degrees. After about 2 hours of cooking the scent of that heavily peppered, delicious beef will be floating through the air. Things always seem to taste better if you hold back your urge and wait until everyone is seated. You'll have more than a few people remarking on that absolutely wonderful scent coming from your oven, count on it. If you have other items that need cooking - do them in the microwave or on the range.
Baked potatoes work out nicely in the microwave and so do other veggies.
Just read instructions for the veggies and grab a local cookbook if you aren't sure of timing the potatoes so they are done when the beef is done. Depending on how well you want your roast cooked, you could pull the roast out of the oven when the meat thermometer shows 165 degrees. A meat temperature of 165 should turn out to be medium on the outside, medium rare on the inside. You do NOT want it to be lower than 165 degrees. Many times when you pull it out at 165 it will climb to 170 at carving time.