The Germany NRS (v. 3.3) mentions that:
“Once per game, if Germany declares war on the Soviet Union, all German land and air units get +1 Attack and all Soviet units get -1 Defense on all rounds of combat and subsequent blitz. The Soviet Union may not Attack more than one German-owned land zone on its next turn. (Germany does not get this bonus if USSR declares war first).”
As you pointed out, if the Soviet Union declares war first, it does deny Germany’s suprise attack special ability, but the USSR will lose the immediate boost to Wartime income that comes with the Germans attacking first.
It’s a balancing act between striking first and reaching full income. The closer you are to the USSR Wartime Income, the more you can afford to declare war first. A lot depends on the luck of your Sleeping Bear rolls.
Overall, as the USSR, I think it’s best to plan that Germany will probably stirke first and not commit yourself to declaring war first at all costs. A thin line of militia on the border should limit the damage that Germany can do with its suprise attack.
Orel-Kursk is a good place to mass your Red Army out of arm’s way and keep your options open for a possible counter-attack. You can also withdraw your Kiev factory and scortch earth its airbase. After that, not one step back!