Guys and Dolls is a fantastic show, but yes very proppy! Clear Props Lists, Setting Lists, Running Lists etc. will be really important.
1-Our set involves a turntable. How do you tape this out (silly thing I know but vital since lots of set pieces will be 'on top of each other' as the table revolves).?
As others have said the normal way is to tape out the turntable/ revolve in one color and then use lots of other colors (labeled and displayed with a key somewhere prominent in the rehearsal room!) to tape out the various furniture for other scenes.
2-We are also using machine operated moving platforms, what advice can you give?
Yep, as others have also said, the main thing here is safety. What you may have to do is work "clearances' into your book/ cueing. For example automation cue 4 (which could for be your platform tucking on and turning 90deg) you would warn/ stand-by at which point one of your ASMs or Automation Assistants would go and take position by the truck/ area. Then when you call it you would go something like "Automation Cue 4 clearance" ("CLEAR") "AUTO 4...GO". They can then watch its movements and report back straight to the operator or you if there are any problems. You are also could have e-stop buttons on the prompt desk for automation so make sure you locate them and work out what's what - if applicable, so in an emergancy you know what to do. Likewise a full briefing to cast and crew on what to do if there is a "Show Stop" will be required. Automation is the No.1 (by far) reason for show-stops in the West-End! In-fact most shows only ever stop for automation problems in the west-end.
3-During music rehearsals if I have no paperwork to do, is it ok to...read a book and such?
I find it hard to believe that you will never have anything to do, there's always calls to write up, rehearsal reports to write, blocking to tidy up, and a plethora of other jobs to be done in the book but failing that I would agree it's completely unacceptable to read/ do other things in rehearsals. If there's nothing else to do then just practice following the score, knowing it intimately will be good practice for when your Lighting Designer whats to put a cue on every other upbeat! Also don't forget to listen out for any cuts. The Musical Director can cut repeats, bars or even whole sections just as the Director can cut lines and if this happens and you don't notice you and the LD will be the first to get confused in the tech!
Best of luck, it's a fantastic show!
Sam x