Does ‘and few in the jungle care for those odds’ mean: and few in the jungle are willing to accept such a bad disadvantage. – Yes.
Could I suggest ‘Would that Baloo were here’ = if Baloo were here? – Yes.
If so, why and how could it be? – Maybe I don’t understand this question, Haihao. ‘Would that…were’ is a reasonably common formulaic subjunctive.
Does ‘Down hoods all!’ mean: put all your hoods down!? – Not exactly; ‘All of you, put down your hoods!’. I presume you know that a cobra has a hood which it spreads when it is alarmed or angry.
Does ‘… plunged under the heaps of his enemies’ mean: … threw himself earnestly (into the fighting) under many layers of the monkeys? – Yes.
Is ‘nearest’ a ‘superlative preposition’? How could it be so? - Yes; why not? ‘The ruined wall [which was the] nearest [to] the jungle.’
Does ‘only to disappear to the head in a wave of monkeys’ mean: only to become covered (with monkeys) all over but his head in a wave-formed crowds of the monkeys? – …All over but his head in a flowing wave of monkeys.
Does ‘the monkeys stood three deep on the red steps’ mean: the monkeys stood three circles deep on the red steps (of the water tank)? –Yes.