A good A&A player would generally tell you to build 6-7 inf for each arm unit. This helps you protect the armor and ftrs you have on attack and defense. Remember, infantry = fodder, while arm-ftr = 1-2 punch by one player. When G & J apply it to R it hurts. When UK, US & R(inf only, until you see that the inf you have starting turn X outnumber the inf+arm+ftr G will have after his build on turn X[unless UK & US are shipping inf to reinforce your position]) apply it to G it really smarts!
Mobster, sorry, but you lose in Alaska as I build US inf & arm in W US each turn and move it - US2 to W Can - US3 to E Can - US4 to UK, Nor/Fin, W Eur or Alg.
If you hit Mexico my W US force of 6 inf & 1 arm(minimum, likely extra arm & ftr) hits your force.
If you hit Alaska my W Can force of 6 inf & 1 arm(minimum, likely extra arm & ftr) hits your force. Note: If I’m really worried I’ve flown my bmr from UK to join the attack and land in W Can.