The food portions have declined in size over the years, but I find that the catering's still pretty good. I'll complain bitterly until the cooked breakfast is added to the 'dish' menu, but the bacon roll is tasty and the avocado muffin always looks nice. The drinks are on a trolley, which you usually hear clinking away before it arrives at your seat - you tend to get one drinks run per hour in my experience, so from Wakefield you should get either two or three before arriving in London.
The service you've chosen is booked to be two five-coach Azuma trains joined together, each of which have two small First Class cabins. You'll probably find the service to be friendly and attentive. There's a national reservation system used by both LNER and Trainline, so yes the seats are yours.
However ... five-coach Azumas have just the one private table for two people sat opposite each other. There is also an 'airline' style row where there are two First Class seats adjacent to each other (E1 and E2, M1 and M2), but those seats aren't next to a window. Unfortunately, from previous experience, some folks will often take the sole table for two if you're not joining at the starting station - despite the fact it's reserved later on in the journey. All you're able to do is politely ask them to move, else you'll have to sit at a table for four.
Hopefully this shouldn't affect your enjoyment of the trip too much, but it is worth mentioning that if tables for two are very important for you, the other type of train LNER uses on that route (the older InterCity 225 'electric' trains) have considerably more of them - 18 in all. These trains all start and end their day at Leeds or York, so they tend to work (almost) consecutive services southbound and then there's a gap. There's nothing around 09:29 but the 08:14 and the 11:28 from Wakefield are booked to be one. It's probably not worth the cost or the inconvenience of changing the train you're booked on to guarantee a table for two, but worth mentioning in case you do this journey again in the future.
LNER First Class is usually a very civilised and pleasant way to travel, one of life's little pleasures. Hope you have a good journey.
