You can camp wild pretty much anywhere, except in built-up valleys and obvious places like that. I've never had trouble finding somewhere and never been turned down when I've asked farmers. Romanians are lovely, friendly people who simply didn't deserve their history.
Sadly, for all their friendliness, they are appalling drivers. Given that the roads are often also raddled with deep holes - although they are slowly being repaired - riding on Romanian roads can sometimes be like taking part in a bullfight.
Many roads, though, are beautifully empty. But which they are can be unpredictable. Roads prefixed with an E are generally horrendously busy, being international truck routes to the Black Sea. But some can be deserted and charming. I never found a way of guessing which would be which, although your living there will give you local knowledge pretty quickly.
Bucharest to Istanbul will be one of those busy roads if you take the coast, especially in summer. The Black Sea is a big holiday area built up in the communist era. Take a more inland route through Bulgaria, though, and you should have little trouble. When you get to Istanbul, avoid the obvious route from the west. It is four lanes in each direction with multiple exit junctions. Use either the ferry from the south or use minor roads that will bring you to the Bosphorus north of the city. That way you will have just ordinary city traffic going into Istanbul, with occasional relief from bike paths along the water's edge.
No problem with being a foreigner. Romania is open to the world and proud of being in the EU. Turkey is famous for its care of strangers and Istanbul is a giant tourist mill.
Getting food can be a problem in rural Romania. Shops are small and hard to find and tend to supply only what a barter economy can't provide. Hotels are cheaper than in western Europe but prices have risen a lot, especially in cities. Don't expect marked bargains.
You'll be warned about gypsies. I have never had the slightest trouble and I suspect their reputation comes from bigoted people who've never actually met any.
Hope that helps