The way I see it.
You cannot fly IFR into an unmanned VFR Airfield. (Not even into a manned VFR airfield) You would have to cancell IFR at some stage before landing, normally when a landing is assured. This is normally done when you have field in sight and reasonable assurence exists that your flight can be completed in VMC conditions.
You could depart from an unmanned VFR field as an IFR flight, keeping in mind that you are responsible for your own seperation untill in controlled airspace. You need an ATC clearance however to enter controlled airspace!
A visual approach is an extension of a instument approach, where the instrument appraoch is either wholly or in part flown with visual reference to ground. That means that you could be cleared for a V/A, visually position to a final approach fix, and then intercept the ILS. A visual approach is strictly speaking still an instrument approach, flown in VMC conditions to expedite your arrival.
It is a hot debate on what the correct missed approach procedure would be for a V/A. In very few cases is this actually published around the world. Should you fly a visual circuit after the M/A? Or should you follow the missed approach for a published I/A, if so, which one? I trust that this debate will be a neverending one, until such time that its actually published in the relevant docs. In the meantime, its important to be clear about your intentions when in this situation, letting ATC and also other traffic know exactly what you're doing, as everybody has a different opinion on this matter.
Hope I could be of help...
Best regards.