Thats entirely up to you. There's no right or wrong amount of likes to order, it all depends how much exposure you want on your photo. For instance, if it's an important photo or video, or if its a contest or announcement, it would make sense to purchase a large amount of likes and comments for that post.
It is recommended; it looks more natural to have both likes and comments on a photo, as it is the most accurate indication of engagement. If a photo has a large number of likes and very little comments, or vice versa, it could look strange or unnatural.