1.I think you can use the f6.3 reducer on the c6 to get a 945mm focal length which is ideal for small to medium dsos and is a little easier on the mount.
2. Yes but it may not be accurate enough you may wish to use phd2 drift alignment or
D.A.R.V alignment if you can see the meridian in the north (for the southern hemisphere)
3. I don't think that will give you good results, there is a f3.3 reducer but it's only for eaa.
4.It is possible to go without a guider but it is not recommended without a premium mount at these long focal lengths, an OAG would be ideal and should be possible with your 224mc.
5. No filters are necessary but if you have significant light pollution you might find the contrast improvement worth it for the compromised star colours.