There are lots of routes that you can take-
We have never felt the need to go as far as Istanbul.
in the past we have had the truck loaded up with small personal items and sailing stuff and has always been ok, just be prepared to have to unpack at certain borders ( maybe )
Remember to check with whichever countries you choose to pass through wether they require you to obtain a " vignette" to enable you to drive on certain roads in that country. This is really important as There are hefty fines and penalties to pay immediately ( at the roadside ) if you get caught out without a relevant pass!
Remember to pass through France you need to carry your OWN breathalyser equipment as well as a European road safety set including warning triangles, high vis jackets for both driver AND passenger.....And depending when you will travel some countries will insist on snow chains, fines for non compliance again.........
Can advise on routes and places to see/stay en route if you're interested, we always take our time and visit loads of exciting and interesting countries..... Serbia and Croatia and Bulgaria ( but stay out of Sofia and Plovdiv ) recommended!