So you know how big a king size quilt is, right? You've laid one out on the floor to really grasp the dimensions? Look at what you're going to be wrangling through your little domestic sewing machine? Or, if not you, then how much you'll be paying someone with a long arm to quilt it? Know how much that costs? Per quilt?
Now, I really didn't mean to terrify you. ;-) ;-)
A king size is about 95"x95" (more or less). So if you have some plan for 49 blocks, that's a 7x7 layout, which would mean each block is approx 13.5 inches finished.
Are these little grandkids - why would they need a king size? Or adults? Because if you make a king-sized quilt, you're basically expecting it to go in the master bedroom, and personally, I think that's a bit presumptuous. Maybe it's not their decor, or the SO really isn't going to be thrilled.
So how about a wall hanging or a throw for the couch? That's much more manageable, and useful. And they'll be better able to show it off. You can mix and match photo blocks with pieced blocks.
But if you want it to be a memory quilt, and because you're new, I'd go with a wall hanging/couch quilt first. That's definitely doable.
Actually, I really like the idea of wallhanging, say 36x 48. You can get experience piecing, printing photos, joining block into rows, putting borders on, and possibly even quilting it yourself without being totally overwhelmed.
And, for full disclosure, my first quilt was king sized. Know where it is now? In a bag in a box in a closet in the storage room. Unfinished.