Questions thus far:

1 What type of electrical cable, and voice cable, are required for overhead suspension,
given the application (note the 3-way switch requirement)? Is the cable self-suspending,
or is some type of separate weight-bearing carrier required?

Quadplex cable is three insulated aluminum conductors wrapped around an
aluminum clad steel reinforced conductor that will serve as the
Equipment Grounding Conductor (EGC) as well as being the messenger that
supports the other three conductors.

2 Can the electrical and voice cables be run in close proximity?

NO! It is dangerous to do so and it will induce noise into the voice
circuit.

3 Is a service disconnect required on the house end of the run, or can I simply use a new
breaker in my 200a panel?

You will need to provide a service disconnect at the garage end of the
circuit but if you have a pair of three way switches that will open all
of the ungrounded conductors that is all that is required on residential
property. No separate disconnect is required at the house end.

4 Should I use a 15a GFCI inside the shed, or a circuit-breaker type GFCI in the 200a
panel?

I would use the GFCI as the first receptacle in the shed in order to
avoid nuisance tripping due to leakage current in the overhead span
during wet whether.

5 What gauge electrical wire is appropriate? I estimate the entire run, from the breaker
to the farthest point, at 115'.

If the entire run were going to be the aluminum triplex then you would
need six gauge to avoid excessive voltage drop. I would imagine that
eight gauge would be fine since it is less than half of the total run
length. I assumed a twenty ampere total load for that calculation.

6 How high for the suspension points? How high for the lowest point on the overhead run?

225.18 Clearance from Ground.
Overhead spans of open conductors and open multiconductor cables of not
over 600 volts, nominal, shall conform to the following:
(1) 3.0 m (10 ft) — above finished grade, sidewalks, or from any
platform or projection from which they might be reached where the
voltage does not exceed 150 volts to ground and accessible to
pedestrians only
(2) 3.7 m (12 ft) — over residential property and driveways, and those
commercial areas not subject to truck traffic where the voltage does not
exceed 300 volts to ground
(3) 4.5 m (15 ft) — for those areas listed in the 3.7-m (12-ft)
classification where the voltage exceeds 300 volts to ground
(4) 5.5 m (18 ft) — over public streets, alleys, roads, parking areas
subject to truck traffic, driveways on other than residential property,
and other land traversed by vehicles, such as cultivated, grazing,
forest, and orchard

7 For safety and durability, I want to conduit the runs at both ends, from the suspension
point to the entrance point. What kind of junction is appropriate between the pipe and
the overhead cable? Between the pipe and the interior cable? Can Romex be run through
conduit, or must THHN be used?

Install service heads on the tops of both raceways. Splice the quadplex
to the conduit wiring using pre insulated patent splices that are
available from any decent electrical supply house. Each conduit will
terminate in an LB that connects to a Jbox located inside the building.
Make your transition from the raceway wiring to cable in the junction
box. It is currently a matter of debate whether it is permissible to
run NM cable in conduit. I think it is a poor practice at best and
would recommend avoiding it.

Best regards,

Tim ==

Other questions please ask.
--
Tom H