1.) I boot hyperspin from startup and the best resolution I found it to work in is a single monitors resolution in windowed mode (so that it fills the center monitor) I then have a black desktop and hide the task bar.
If i select the full screen resolution of 3000*X1920 it looks horrendous. Is there a way to set the full screen resolution to display just on one monitor ? couldnt find a solution anywhere.
I don't have an answer for that one.

2.) One of the guys on here modified the joystick symbol in hyperspin to a steering wheel, where can i get this from and how do I change it?
That was mbasile35. You can try PMing him. It's up to him whether he wants to share or not.
http://forum.arcadecontrols.com/index.php?action=profile;u=30996He changed it to hyperpin mode to get the wheel on the bottom instead of the side.
3.) N64 gaming, what controller plugin do you guys use? Is there any tweaks you can suggest? I didn't find the controls via the wheel amazingly accurate.
Not sure which one I'm using, just used whatever the default one in Project 64. Tweaking the sensetivity and saturation in Logitech Profiler helps some, but I've never been able to get any of the console emulators tweaked as good as I think they should be. I don't know if the fact that these games were designed for gamepad joysticks is the problem.
4.) Psx with the steering wheel, to play Gran Turismo etc, what emulator and plugin do you guys suggest? I am using Epsxe and it appears to use digital controls, so with the wheel this is kinda horrendous 
You have to press F5 after the game starts to activate analogue mode. You'd be surprised at how many of the popular driving games didn't have analogue support because the analogue gamepad didn't come out until a few years after the playstation did. An autohotkey script could be made to automatically post F5 if playstation games are important to you.
5.) Is it worth setting up demul and Dolphin, are there any worthwhile games to play on here that work well with a wheel?
I think so. I have Crazy Taxi and Jambo Safari running on Demul .5.6 on my driving cab.
Demul .5.7 adds the atomiswave games Faster Than Speed and Maximum Speed, but I don't know how well they work with the new directx11 plugin since my driving cab has XP. With the legacy plugin, it's real glitchy and the track disappears. I have a leaked WIP version from before they switched over to directx11 that works fairly well, but it required a lot of workarounds to get working.
In Demul, the pedals must be set to combined which is different from most other emulators and games.
Set up a profile in logitech profiler for each emulator. It will automatically load the setttings whenever the emulator's exe is launched.
I'm using NullDC for Dreamcast games, but they probably work just as well in Demul. As stated above, I've never been able to get the controls tweaked well enough for my taste (maybe just need to invest more time), but Hydro Thunder for Dreamcast is reason enough to set it up.
I've installed Dolphin and tinkered with it, but haven't spent a lot of time with it yet.
It seems well worthwhile. Simpsons Road Rage is a hoot!
The burnout series for gamecube supposed to be really good, but I've only played a couple times to test it.
I'm sure you've seen it already, but if not, there is lots of info in the thread linked in my sig.