Remembrance of the second world war is an almost cult-like phenomenon in Russia and the Former USSR. Every town and village has a monument to it. So I think you'd need to be a little selective of where you go as you could literally spend months looking at various monuments.
Volgograd is an absolute must. I would also try to return to the EU via Belarus to see Brest, which is in my opinion the second-most impressive WW2 monument in the Former USSR (after Mamayev Kurgan in Volgograd).
There are also the 11 other '
Hero Cities' with notable WW2 connections. I've been to all of them except Novorossiysk; Kyiv, Tula and Smolensk stand out.
Near Smolensk is Katyn Forest, and a big monument to the Polish officers killed there by the NKVD.
In Belarus is a moving Soviet monument complex known as Khatyn.
There is also a monument to the Kursk Tank Battle somewhere near the city of Kursk, though I have not been there yet.
Near Vladikavkaz is a monument marking the furthest which the Axis Forces got towards the Absheron oil fields near Baku.
If you are interested in older 'war' history, there is Borodino Field between Smolensk and Moscow where the Russians fought Napoleon in 1812.
Earlier still is Kulikovo Field south of Tula where a decisive battle was won against the Golden Horde in the fourteenth century. Also on my list...
As for safety, Russia is very safe, nobody will hassle you when wild camping, people are kind and very helpful though you're unlikely to find anyone who speaks more than a few words of English outside of Moscow and St Petersburg.
You could follow the Volga south to Volgograd, then loop around through southern Russia (Voronezh, Kursk), enter Belarus and exit to Poland.
Hope this gives you some ideas
EO