A set neck doesn't make a huge difference to sustain in my experience - the wood used in the body is more significant. Big lumps of mahogany or maple will create more sustain than alder. However, the guitar will weigh a lot more. I had a Les Paul DeLuxe and a Yamaha SG 1000 and they weighed a ton !
If you want infinite sustain get an ebow
I've found the strat type bodies to be the most comfortable for me. Then there's the neck to consider (size / the type of wood used in the
fingerboard), the action etc. A tremelo arm is another consideration. There's a lot of 'snake-oil' attached to guitar tone in general, you've got to
make your own choices. For example, there's a ton of amplifier / cabinet modelling software out there and I've heard great reviews of some of them and tried them out and thought they were awful.
In terms of pedals, I would personally recommend a volume pedal, particularly for 'ambient guitar'.