You can't add dining to room only. Even AP holders have to book a package, even though it is a ticketless package. This is relevant because the deposit, cancellation, change and payment rules are different for packages than they are for room only. If your friend books you on an AP ticketless package, the reservation will follow package policies, not room only policies. Since this trip is last minute, cancellation and payment policies may not concern you. If you want dining you will need to book a package. If you go the ticketless AP package route, the annual passholder must present his pass at check-in. I believe he can book up to 3 rooms.
Not only that, but you cannot add dining at check-in. It must be done no later than 3 days before you arrive.
If YOU book the package, and your friend is on it, in order to get dining you have to buy him the same tickets you get.
Yes, you will need restaurant reservations if you select a dining plan with table service meals. You may still be able to get into the less popular park restaurants, or the restaurants in resorts that are not near parks. At a park like MK, which has only five TS restaurants (one of which costs 2 credits) if you want to eat in the park, you should probably have a reservation.