[DonnyKong]

Even if gods are imaginary, they still dominate humanity.

maybe, but as Buddhists, we enter a different kind of life...

...it was sort of inevitable for humanity to create in such a great presence of illumination.

maybe, but generally most religious founders did not recommend ornate temples, be they Moses, Buddha, Jesus or Mohamed (PBUH)

But did he not teach of prior buddhas?

maybe but dubious, although some scriptures mention so. but buddha was Sammasambuddha (Perfectly Self Enlightened without a teacher who starts the Buddhist religion). thus any prior buddhas were not an influence. to regard the Buddha as having a teacher means one does not have faith in the Triple Gem

...Didn't he claim to be a reincarnation of Manjushri or some other yogi?

definitely not

...I wonder if Buddha relied on a 'higher power', at least in some point in time in his revolutionary life.

Buddha-To-Be was part of the samana tradition that practised aseticism. they relied in self-reliance. but when Buddha learned to tap into the 'Nirvana Stream', he certainly relied on a 'higher power', which is something natural, like gravity or homeostatis. if we actually meditate ourself, we can be without doubt about this higher natural non-personal power

...I just wonder how Buddha founded peace and harmony with the ancient Hindu dieties like Vishnu and Ganesh. .

a mind at peace is at peace with everything. it understands there is difference in the world and is at peace with that difference. it does not try to change that difference unless it knows with certainly that difference wishes to & can change

...So for the topic, I say, expect all the gods to come into your favor, because you are coming into alignment with them as a bodhisattva.

if you mean as a bodhisattva we cultivate metta-karuna-upeka towards these mundane 'gods', the answer here is certainly 'yes'

kind regards