Hunter's job for Burisma was shady as fuck, no doubt about that - and it was far from the first time that Hunter or his uncle Jim abused their father/brother's name to get a lucrative job or business opportunity.

However:

1) As I mentioned before, while Joe did brag about getting the top prosecutor in Ukraine at the time fired, the reality was that Shokin was fired after joint pressure from the US, the EU and the IMF - with all of them arguing that he was blatantly failing to investigate corruption, both the pre-existing investigation into Burisma and other ones. In the end the Ukrainian parliament voted to fire him after they additionally saw reason to believe he was personally corrupt himself - though that was only three months after Biden's visit so his version of the story seems rather embellished. In other words, the international community pushed to have him fired primarily for the benefit of Ukraine itself and with the full expectation that whoever replaced him would achieve more in terms of the Burisma investigation (as indeed they did - Burisma ended up paying millions of dollars to the Ukrainian government to settle the charges). You need some pretty crazy conspiracy theories to spin that into 'he was fired by Joe Biden because he was investigating Burisma/Hunter'.
2) When you say 'bribery' do you just refer to the salary Burisma paid Hunter? If you mean something beyond that, or that Hunter actually achieved anything illegal or illegitimate for Burisma in exchange for said salary, I haven't seen any proof of that - Shokin getting fired doesn't count obviously, considering the above.
3) Joe getting money - haven't seen any proof of that either.

See also this article from December 2015, at the time of Joe Biden's visit, rightly pointing out that Hunter's position at Burisma was rather undermining his father's / the USA's credibility in criticizing corruption in Ukraine. I'd go further and argue that the Obama administration should have kept Joe Biden away from anything to do with Ukraine as soon as his son got that seat on Burisma's board. But just because they didn't, still doesn't automatically mean that either Biden actually did anything illegal. https://www.nytimes.com/2015/12/09/world/europe/corruption-ukraine-joe-biden-son-hunter-biden-ties.html

'As part of legitimate foreign policy' - as opposed to 'as part of oppo research for the president's next political campaign'. Although really, if you read the released transcript of that famous call, it's more like Trump doing his usual rambling on with nonsensical word salad vaguely inspired by some rumours he heard left and right. Based purely on that transcript, one would say he deserved impeachment more for rank incompetence and being a national embarrassment than for actual corrupt intent. Though on that note, I admit Biden's self-aggrandizing claims about getting Shokin fired back in 2015 were an embarrassment to his office as well.

Once again, what proof? Moreover, the basic (and admittedly suspicious-looking) facts regarding Hunter-Burisma-Shokin's firing, which Trump alluded to in his call, were common knowledge long before day one of Trump's presidency - his DoJ had had 2.5 years by the time of this call to find proof and charge either or both Bidens if they could prove any crime was committed, which they didn't. But where US law enforcement was unable to find anything, somehow we're supposed to believe that Zelensky and the weak, often corrupt authorities of Ukraine could? That US law enforcement might've needed assistance of some sort from Ukraine, sure, but in the end if we're talking about Joe Biden supposedly having received a bribe, there's gotta be a money trail in the US as well, same thing for any illegitimate/illegal advantages obtained for Burisma by either Biden. Most of the investigation would always have had to come from US law enforcement agencies.

If Trump had no better ideas than to make some vague requests of Zelensky instead, it's presumably because there was a lot of smoke but no actual fire, which he either knew or should have known if he hadn't been too lazy to bother reading/studying up on anything.