I see a few things; first, I want a railing at the edge of the steps where the countertop starts. Something to alert someone walking on that pool decking that they are about to stray into an unprotected 3' drop. I can imagine a very attractive wrought iron railing made for this.
Second, as was mentioned, take a look at the dimensions of the lower patio area. I assume you will want seating there to admire the water falling. There are rules about how big an area needs to be to comfortably seat X number of people. As I recall, for table seating, take your table size and add 4' all around to allow for chairs to be pulled out and sat in and also walked around when people are seated. That is minimum. 12'x12' is about right for a small table, 4' square, seating 4 persons. I am assuming the covered patio at the house is about 12'x5' based on the doorway being about 3' wide.
If the area will be conversation area, then you need to add the sofa and/or chairs and table and side tables and so on as well. You can fit a decent conversation area for 4 or if you want to have 6 you will want it bigger. I have a patio area for 7 in a U-shape; sofa seating plus 4 arm chairs, small coffee table and tiny side tables in a 12'x12'ish area but there is no walkway behind any of the seats as they snug up to the edge of the flagstone and the approach is from the open side of the U. And my furniture is not bulky, thin aluminum made to look like bamboo. Some sets are huge so beware.
The lower area in your plan could be used this way as long as you have enough room for people to walk comfortably and safely to all the chairs, allow 3' walkspace between chairs and water, min, where the chairs face the water. If chairs are back to the water, as a dining table, you may need 5' from the table edge to allow 2' for the chair and 3' more, 4'd be better.
Third, you could consider a couple of chairs up by the spa. Or one or two chaise lounges. At least one somewhere, someone always wants to sunbathe -- where is the afternoon sun coming from? If it were near the spa then there would be a place for folks to drop their towels. So look at the size on either side of the spa to allow a chaise if that is where sunbathing might be best. Kinda looks like the step into the water there is on the wrong side, maybe that is not what it is, I cannot really tell.
Finally, I'd like to see some seating at the grill that faces the cook that is not in the water. I think there may be too much unneeded floor space in the cook area. Changing the dimensions there might be helpful. I suspect that a lot of the time you are cooking out there will be for people who are not in the water while eating. How many will there be and where will they eat if not in the water? If the upper decking was larger and the grill area was smaller and slid to the lower left a bit, you may have room for a dining table. Beware of the view from inside the house if a table is set there. You have nice windows at that patio at the house and the view from there is probably quite important.
