For your roast beef, my best advice would be to find a local butcher who you like and trust and ask them about their cuts.
It is quite difficult for us to give you suggestions since we don’t know what is available to you in your region or your budget.
Eye fillet, round, rump or even prime rib are all good choices for roast. But at least where I am, some of these can be quite expensive. A big roast dinner is usually reserved for occasional meals, we don’t have a big roast every day. So perhaps you could spend a little bit more on the meat for the occasion.
I strongly recommend you get a meat thermometer - so very handy. Used correctly, you can monitor the internal temperature of your roast to ensure that it doesn’t get dry and it is cooked evenly and properly.
Also you should think about other kinds of meat. Lamb is very nice when roasted. Same with pork (but I don’t know about religious tenets here).
Good luck!
