I think it R1 purchase also depends on R1 combats. If you tend to attack WR+Belo, you won’t lose too much infs so that some arms buying sounds good to maintain the ability to threaten multipul front line. If you tend to attack WR+Ukr or even WR+Ukr+Belo, you might lose a considerable inf base so that probably you need to buy more inf to solidify your front line. Or, if you want to do the Norwegian Gambit, in case of a failure, you could not afford to be aggressive. In case of a success, some degree of conservativeness doesn’t matter. In either case, all inf buy is not a bad idea.
My aggressive buy is 3inf+3arm and conservative buy is 6inf+1arm and save 1ipc. I do not prefer art, my understanding is that the initial 2 art is enough. From R2 onwards, all USSR could do is trade territories to gain ipc and slow down G’s stepping forward. inf+intial 2 ftrs are effective to trade. inf is cost effective to defend crutial territories like WR. arm is effective to generate threats. art is inferior than inf to defend and in most cases, art is no more effecient to attack than arm. The only reason I would like to buy art is that I’m considering a light attack to trade units with G to disturb his plan and probably to snip some net ipcs both from and after the combat. Sure G will counter attack, but I would only lose some art instead of expensive and important arms.