RE:
I am proposing to use a professional rigger to supply and terminate the components.
So, you will measure , give the rigger the lengths and have the rigging made before hand?
I'm happy setting the rig up myself, actually I would prefer to.
What do you mean by "setting the rig up"?
Has anyone done this? Is it safe to go up the mast on the main+spin halyard with the rig only held at the partners and D1s? How did you do it?
Is it safe to go up the mast on the main+spin halyard with the rig only held at the partners and D1s?
I would say no. You could use two halyards to support the mast and one to haul up on.
I would not go up an unsupported mast even if it was partially done. Think about hiring a cherry picker. Safer, easier and faster.

Many years ago I re-rigged my 36 foot double ender in Singapore at anchor.
She had mast steps.
I measured all the rigging and had it made up 30 cm too long with the top end fittings swagged on.
One by one fitted the shrouds at the top. Did I mention that I had mast steps?
Cut them to length and fitted Sta Lok fittings to the lower ends.
The rear stay was split with a set of triangular plates. Had the top section made up and the two lowers made long.
Tied off the main halyard and spinnaker halyard astern and did the rear stay with Sta Lok fittings.
Tied off the foresail halyard and spinnaker halyard forward and fitted the new forestay.
Didn't have a small battery powered angle grinder back then so the biggest hassle was cutting the rigging wire with a hacksaw.
Sta loks are expensive but they can be reused.

gary