Thanks everyone, for the responses. I have been off the forum for a couple of days because we set the tub and repaired the hole yesterday, and last night I was exhausted. So I am just seeing some of these responses today. I am happy to announce that at Bill and Mongo's strong suggestion, and my own gut feelings and common sense, I had decided by yesterday morning to definitely go with the concrete. It just seemed to me that if concrete was there originally, it should go back in. The plumber's viewpoint was once the slab had been broken into, its former strength could not be restored by using concrete. Another guy said that mortar would 'adhere' better to the old concrete and was more supple... so if there was any 'movement' under the slab, the mortar would have more 'give' and be less likely to crack. The plumber seemed convinced of his viewpoint, but he was flexible. I told the plumber that I preferred concrete. He said OK. He got the concrete to set up quickly by 'layerin' it. It worked very well. I hope that's a good thing. Ventupete, the 'rebar' idea is brilliant, and you're right, he would have thought it was overkill. The plumber thought it was overkill to have my exterminator over there to treat the soil in the open hole. You asked about the hole? It was kind of centered under the tub, with part of it extending out past the surround, in order to rework the plumbing. So the greater part of the tub was always resting on existing slab. BTW, does everyone know that exterminators recommend treating ANY infraction in a slab? They say that termite (subterranean insects that they are) will come up through even the tiniest hole in a slab and will be 'pigging out' on the studs in your home...you won't know a thing! If you are adding on to your home, treat the soil in the piers of your addition, BEFORE it is poured. True story. It happened to friends with their add-on. Thanks again for the input. We successfully have a tub in place. I would call that a small miracle. :)

You'll want to rent a plate compactor for the base. A hand tamper is fine for tight corners and places where the compactor can't go but unless you're a World's Strongest Man champion you'll have a hard time getting great compaction on that big a walk. Especially using bigger slabs, you don't want voids showing up underneath them or having them move. No need to compact your bedding layer. You want it loose to help level each slab with its neighbors. Just give them a whack with a rubber mallet. I'd run the 3/4 minus 12" wider than the finished walk on both sides, compact it, and spike in paver edge restraint. By creating a fixed edge that the pavers can't move beyond, you make it a little less likely that the pavers will shift within the walk.

Louis, I've never seen precast slabs that big but they may be available somewhere. Generally for something that big people cast them in place. If you're wanting several of them I think doing it that way is the best option, they can be aligned and leveled easier and more precisely than precast ones and I don't think the cost would be too great. In CA it's pretty easy to find concrete guys who are willing and able to do a job like this.

Are the triangular, mauve colored gravel mulch areas what you're calling "planters"? I would eliminate them. They seem much more like an impediment than an element of interest. Regarding your paved area edge, I'd simplify. A clean, simple shape would be better looking and easier to use than one with busy flairs (waves and meeting other surfaces at oblique angles.) We're not in a good position to determine if you can keep or get rid of the step. The latter would be preferable if you can do it, but since the patio and pool already exist at their respective elevations, you have to accommodate what you have. Determine the actual difference in elevation in order to know what's possible. If you need to keep two levels, I'd recommend exploring the layout geometry again. But you'd need an accurate plan to work from. The one above shows the pool nearly touching the patio cover. In the picture it looks like you have at least 5' or so there.