I think a BIG mistake is to get attached to the word "airway". This is a peculiar UK PPL tradition, where instructors use the word "airway" to basically scare students into avoiding Class A airspace. In much of southern Europe, you fly VFR on published airways (IFR routes), because that's where their simple-minded ATC expect to see traffic.
All that matters, when it comes to pilot privileges, is the ICAO airspace
class i.e. A,B,C,D,E,F,G.
An "airway" is just a line on the map; it means nothing re pilot privileges.
You cannot enter A without an IR, unless it touches the ground in which case it can be done under SVFR. In practice, a non-IR pilot (or for that matter a pilot who has no license whatever but merely can fly and knows the protocol) could ask for an IFR clearance and - outside the UK, anyway - he would probably get it. But his acceptance of it would be illegal.
And yes to be legal you need to carry the equipment specified by the airspace owner for that flight rule (VFR/IFR etc). Again, no way to check this apart from a ramp check, though a non-8.33 radio might eventually expose you if you were flying above FL195
The filing of a flight plan is another subject. VFR flight plans are generally never looked at by anybody so filing one doesn't get you any clearances.