As I wrote in connection with the last conversation on the Syrian situation, Russia is protecting its Mediterranean naval base and now air base as well in the Alawite enclave on the Syrian coast. They are essential for the Russians to project power both west into the Mediterranean world and east into the Middle Eastern morass. Putin is in the midst of a frantic orgy of power projection in all directions, but particularly to the west against Europe and to the southwest against both Europe and Asia. Since the seventeenth century Russia has been proud to be both a European and an Asian power. It was humiliated in Asia by the Japanese in 1904-5 and subsequently, botched its heaven-sent opportunities in the region after WWII. Putin does not intend to repeat those errors.
Unlike the Soviets he will strive to retain an informal alliance with China, collaborating with that power wherever possible and profitable. He needs no-one else so long as the US is led by the bunch of fools that has been leading it for years. Iran, in the eyes of Moscow, is a pawn, albeit an important one, as is Turkey. Both can and will be manipulated by the Russians as they see fit.
Those too timid or shortsighted to avoid exerting military influence in a meaningful way (that is not by the occasional bombing raid) will always be trumped by those that are not. Hezbollah is another pawn and much less important. It will be used if useful and discarded if not. The same for Assad. At this point he is in his position entirely due to Russian and Iranian bayonets. They will support him or discard him in accordance with their interests.
The wild card here is Israel. With the most powerful armed forces in the Middle East and nuclear weapons Israel is not to be ignored. But if not ignored, what then? That depends again on how Russia sees the Israeli factor, as favorable, unfavorable or neutral. Iran is ideologically blinded from treating Israel rationally. A witch’s brew? Indeed, except that in this case it is a wizard’s brew, and the wizard is Vladimir Putin, masterfully playing an objectively fairly weak hand. But a weak hand backed by will will always trump a better hand held by those devoid of will.