I've been doing extensive web research and reading many of the
excellent posts here (thanks to all) and have become absolutely sold on
PEX (no connections/joints behind walls) for my pipe replacement
system, especially given the challenges of re-running pipes through
this large masonry house.

As a background to some of the following questions, allow me to explain
the basic configuration of the home. The house is a two-story
concrete/stucco structure with, unusual for Florida homes, a full attic
and a full basement/garage. This arrangement, I surmise, will afford
some advantages for access/work space, as the entire upper floor is
accessible from the attic, and the entire lower floor from the
basement. There is, also, an HVAC/cable chase that runs in a straight
shot from the attic to basement.

The main house feed is a 3/4" line, which comes into the house in the
basement at ceiling level. The water heater is located on the second
floor of the home, not the basement (flood zone) or first floor.

My current thinking, if possible and feasible, is to try to have one
master manifold arrangement next to the water heater and to feed all
appliances with homeruns from that manifold. In other words, I'd run
the 3/4" house feed up the chase to the attic and over to the manifold,
and the water-heater run and return would be immediately adjacent.
Then, I'd drop service lines down the second-floor walls to fixtures on
that level and run similar homeruns for first-floor fixtures back down
the chase to the basement and across the basement ceiling and up
through floor to first-floor fixtures.

I had considered using a secondary manifold in the basement, but after
reading herein about hot-water delivery times and volumes, it seemed
counterproductive to pump 3/4" of hot water all the way from the second
floor, through the attic, to the basement and more efficient to deliver
exact line sizes directly from the second floor master manifold to
individual fixtures, based on their specific needs. An added benefit
would be that all shutoff controls would be located in a single place.

In terms of fixtures, proposed line size, and estimated distance from
the intended manifold location, they are as follows:

1st Floor:
3 bathroom sinks, 3/8", 30'
1 tub, 1/2", 25'
1 shower, 1/2", 25'
2 toilets, 3/8", 25'
1 bar sink, 3/8", 60'
1 kitchen sink, 3/8", 60'
1 dishwasher, 3/8", 60'
1 refrigerator icemaker, 1/4", 60'

2nd Floor:
1 bathroom sink, 3/8", 15'
1 tub, 1/2", 15'
2 showers, 1/2", 15'
1 toilet, 3/8", 15'
1 laundry room washer, 1/2", 30'
2 bathroom sinks, 3/8", 50'
1 shower, 1/2", 50'
1 toilet, 3/8", 50'

I would most appreciate it if anyone with plumbing, especially PEX,
experience could comment on the above layout's suitability, given
distances and line sizes.

A few ancillary questions:

1) Since the reason for doing this project is pinholes in copper, I was
proposing to use all-plastic fittings, versus brass. Good idea?

2) Is it necessary or advisable to insulate hot-water lines? If so, is
there any manner to do that, which allows the lines to be pulled
through walls after being insulated?

3) Incidentally, anybody know whether Florida code permits fixture
shutoffs to be located at the manifold, or must I have redundant
shutoffs at the fixture sites?

4) Crimps (Vanguard) versus expanders Uponor/Wirsbo)? Any pros/cons?
Reliability? Is PEX-A of significant benefit versus PEX-B for a
residential water application?

Appreciate comments to above and any other pertinent advice.

Thanks in advance to all.