Bombers are best when they’re massed together, whether you’re using them to bomb, or trade territory, or as fleet destroyers to hold allied transports at bay, so I’d say you’re best not starting up any bombing campaigns until later rounds. I’d wait until the bombers don’t have any good combat options, and until the bombing can have a real impact on the Russians (e.g. when they start to dip below 20 ipcs on income.) Its also nice to give Japan a chance to get in range with some bombers of their own, so you can double-team the target. The best location to land after you bomb Moscow (whether you’re playing as Germany or Japan) is probably Karelia, so its always good to wait until you have that territory well stacked with German ground/fighters to receive the bombers when they’re done terrorizing the Russian capital. Bomber Command Karelia allows you to cover most of the key sea zones around Europe without giving up your position the following round. If the Axis hold Karelia you can bomb Moscow from Germany directly, and if you have Japanese bombers/fighters parked in Karelia as well, they can be used to disrupt Allied fleet movements around UK, by making it harder for the Americans and the Brits to move independently.
It usually takes about 3 or 4 rounds for Germany to secure Karelia, and about the same amount of time for Japan to get comfortably situated and in a position to send some air support to the European theater. Commence bombing at that point, so you can start maxing the damage on Moscow. Both Axis players should still have a pretty heavy purse, so they can afford to replace AA loses.
If playing with intercept rules, I’d just forego bombing altogether and focus on normal combat for the duration. The intercept swings are wild and the potential casualties under the OOB rules make SBR pretty ugly for both sides (attacker and defender.) If you do SBR with intercept rules though, its really important to have landing spots for your escort fighters which is another reason to stack Karelia.
Bombing targets other than Moscow doesn’t usually pan out for me. Ultimately I think you’re better off saving the bombers for the airblitz or fleet patrol, and only doing the SBR thing if it will give you a definite edge in a ground attack vs the Russian capital the following round.