Not sure on the range of B3 but,LTBX-LGKV fuel and clear customs.
If you are exporting the B3, you will need an export CofA and Turkish costoms release etc as the Greeks are still anal when it comes to Turkey.
If you have everything in order, no problems.
Although handling agents are expensive, Greece is where you will need one to save a little time,Olympic usually handle at most Greek airports,although by the time you arrive they will have lost your details,so keep copies of faxes you sent.
There are no good aviation maps in Greece and they tend to use published VFR routes between reporting points,ask the agents for a copy at LGKV,ATC is pants at the best of times, but if you know where the routes are you will save yourself a load of grief.
Try and get to Brindisi LIBR on the next hop otherwise you will have to stop again in Greece(LGKR).
Once you clear Greece you can use the maps you ordered before you set of for the rest of the route and ATC gets better from now on.
I have flown the next bit via Sardinia (Twin engine),you might want to route up through Italy via Genoa LIMJ, can't give you any pointers on where not to land in Italy but some of the guys on this forum did a similar route back from the Olympics in Athens.
LIMJ-LFMT on the coast route, again a published route which you need to know before hand, they keep you slightly offshore so take a life jacket, ATC expect you to know the reporting points.
LFMT-LEBL may be just too far for you,so LFPM may be an option.
If you do stop again in France the French customs will pounce on you if they haven't already at Marseille,especially with a non EEC aircraft.
They are VAT hunting, so make sure you have the correct paperwork or they will impound the aircraft.
Unlike the UK you will need to flight plan every flight, I make a photo copy master of the boxes filled out then all I need to do is fill out the route and timings, it saves time.
Most airports enroute will accept BP card for fuel, or a mastercard etc.
The Italian airports are marginally better than Greece for getting MET,NOTAMS etc, but the French are streets ahead of anybody.
A fair amount of the reporting points for the route are on the IFR low level enroute charts which also cover Greece,these are cheap and a good back up.
I don't know the route between Marseille and Barcelona,but the French are big on Nuclear power station restricted areas, if you bust these areas they will scramble a fighter and charge you for it.
Another good reason to know the published route and have UP TO DATE maps.
I have flown similar routes without handling agents, it can add hours to your trip but it is possible.
Hope some of this is helpfull, have a good trip.
LUP