If you want to roast beef, I would start with a rib of beef as that's expensive, but a million times more forgiving.
Depending on size, it will take different amount of times to cook. But approximately 1kg would be around 60-70 minutes. I usually put it in a 180 degree fan oven so cooking it fairly hard and fast. Rest for at least 10 minutes. 15 is better. I always place mine on a bed of onion, carrots and garlic, season and rub with olive oil.
To roast potatoes, peel and cut to size. A trick is NOT to cut them too small. A small potato can be left whole, large ones cut in half lengthways. Put in cold water and bring to the boil. Boil for at least 5 minutes, no more than 10. Drain and flick the colander around a little so that the bits that are more cooked on the outside get a bit smashed up. You can do this in advance.
The potatoes will take at least 40 minutes. 5 minutes before you want them in the oven, place a large roasting dish with a generous layer of oil along the bottom in the oven to heat up (be generous with the oil as the potoatoes will absorb it You probably want about 1cm of oil. Use cooking oil (goose or duck fat is nice, but save for special occasions). I sometimes add about a 1/3 olive oil for flavour).
Put the potatoes in the hot oil (carefully) turning them all to ensure they're coated with the oil, season with salt and, if you like, some fresh rosemary sprigs, before going back in the oven. Turn after 20-25 minutes.
For veg, I'd agree with keep it simple. Boiled carrots, peas, beans, broccoli etc are all good options and can be cooked a bit in advance, drained then left in the pot to keep warm with some butter and salt.
If you want to make yorkshire puddings, Jamie Oliver's Ministry of Food recipe is pretty much foolproof except do not use as much oil as he says to use - I put just enough oil to cover the bottom of each muffin tin.
For gravy, I'd use instant to start with (and do for normal days. I only bring out the big guns for special occasions!
). While the meat is resting, drain off the bulk of the fat in the roasting dish (if you tilt the pan carefully, the meat juices are heavier than the fat so the fat sits on top and you can use a spoon to get rid of it). Put on the hob and let it heat up, add some wine - about 100ml is about right - then while it's bubbling away make up some gravy granules then add to the pan. Let the whole thing bubble away for a bit while the meat continues to rest. Taste it and add salt if you like. Or a dash of balsamic vinegar if it feels like it needs to have something lighten it. If your meat was very lacking in fat, a spoon of butter can be good (but with a rib roast, that won't be a problem).