I’m very pro-Russian mech myself. They have served me the best by allowing the Russians to quickly position massive counterattacks that force the Germans to back off. In other words, while the Germans might be able to push to Leningrad or into the group of 2ipc southern territories in the early game, the ability of the Russian mech to get into attack range quickly tends to prevent the German army from camping out and collecting Russian IPCs.
Of course–as Calvin notes–Russia benefits greatly by having some offensive units to go with the mech. Personally, I find that building a few tanks to keep with the mech stack, along with some early artillery purchases gives the Russians a mobile counterattack that limits the flexibility of the German player while enhancing your own.
As far as the Russian airforce R1 buy—I used to love this, when the Russians could take neutral territories, as the fighters (place in Volgo) would attack Iraq on R2. With the new rules preventing this, I would probably take Calvin’s advice and use my initial air force as the scramble defense in Novgorod. More air force is good, and probably neccessary, but it may not be needed as quickly as artillery, which is useful to build early so it can be ready to counterattack the front lines R3-R5, etc. Fighters can always be bought later.