I can't imagine how you could lose to Novgorod, literally all of its neighbours invade it right at the start, and they have horrible troops (-1 fire and -1 shock).
In any case, it all revolves around taking your initial cores (especially from Novgorod, who is the only other Russian country which isn't a OPM) by diplo/force vassalazing and diploannexation (so your BB doesn't skyrocket).
In AGCEEP you can keep the horde off you simply by following the events you're given. Meanwhile, Lithuania may get some friends among your former vassals through events, though they themselves have the possibility of breaking with Poland, which would leave them vulnerable. Whatever happens, try to attack them only while they are distracted in another war, with a 1 siege leader, and of course, avoid snow-laden provinces like the plague. If you're quick enough you'll get these while still Orthodox.
Moscow and (far more importantly) Novgorod are really rich. That, combined with your high serfdom allows you to raise huge INF stacks to slay.
The general rule in any war you have an advantage in is to cover as many provinces as possible, for the loot and to make sure the enemy doesn't recover from his initial losses, though the snow may make this a bad idea. With enough troops you should, however, be able to do this to most enemies.
Once the Russians are united and Lithuania humbled, it might be a better idea to settle down, reduce your BB (as you won't be getting any more breaks and increase tech spending (perhaps infra 1 and then fully LT until you reach level 9 would be the best route). Eventually you'll turn into Russia and the events will handle your eastern conquests (other than colonization, obviously) quite well, you even get annexations!
From then on it's smooth sailing for the rest of the game if you wipe out Poland in time.
BTW, at least in ACGEEP the event improving your tech group is still there.