1) Does anyone know of a port switcher available to permit a PC & A1200 to have simultaneous connection to one PC style mouse / monitor / keyboard?
The switcher has little to do with it... What you need are the adaptors that allow you to plug PS2 devices to Amiga. I use the Mr Hardware adaptors, and they work fine with my simple Belkin switch.
Mr Hardware Computers2) The A1200 has a scandoubler which fits over chips on the motherboard with a ribbon out to a VGA style output port. Would this be of any use regards question 1 (ie : are there monitor limitations that I would need to be aware of when using this device?)
I'm not familiar with that particular device, but again, it shouldn't be a problem, provided that the signal it outputs falls within the displayable range of your monitor. (It SHOULD, of course, or else it wouldn't be of much use to people, but it never hurts to double-check...)
3) Would it be simpler / cheaper to buy a dedicated two-in-one style tower (Power Tower etc) and stuff everything in there?
I have never priced a solution like this, but I would think that it would be more complex than simply adding the adaptors, since you'd be moving hardware around, etc... Plus, you'd still need to deal with doubling the scanrate somehow... Some windows video cards can take a TV input and display it on the monitor, but it probably wouldn't be as clear as a native display generated by the Amiga.
Plus, there's no guarantee of it being frame-accurate, etc... (It doesn't matter if a TV signal is delayed 1/10th sec before display, but it could really screw up your Amiga gaming experience...) No one has ever answered that question of mine....