Above the transition altitude you need to be at the proper quadrantal rule level and you'd be well advised to tell the ATSU and get a radar service. I usually settle for traffic service as deconfliction gets you vectored all over the sky avoiding traffic unlikely to be a factor.
Almost nobody flies at quadrantal or any other specific levels
If in IMC your only choice is IFR transit and the ATCO needs to know that as he must meet the appropriate separation criteria.
In Class G? Nobody will apply separation in Class G, except to traffic on a deconf service.
Yes but that's a bit brave especially below transition level although above everybody should be at a quadrantal level and therefore vertically separated.
Quad levels to not provide separation. I can still fly up the back of you, etc.
Yes and also agree what instrument approach you are going to use, Exeter do a nice line in vectored ILS and will probably offer it in my experience.
Indeed.