Mr.fixit

You can't avoid going down yourself eventually eg. opening bank accounts, selection of scooter/car, etc. Nobody is going to do it free for you unless you pay (tell me if you need & I can recommend some friends), so it is best to still do it yourself. I can give you some ideas if you are new to Phnom Penh:

Banks: You might consider going to foreign banks that are normally "foreigner-friendly", ie. speaking reasonable level of English. You can try ANZ (but they have a minimum sum to maintain otherwise a bank charge applies), Cambodian Public Bank (for their extensive branches and interest-bearing current accounts), CIMB, Maybank, etc.

Visas: most travel agencies will be able to handle them. You can find plenty of them along the riverside.

Insurance: Cambodian Public Bank has an insurance arm at their main branch

Scooter / car: depends on what you need, new/second-hand and your budget.

Of course i would pay for it.
And of course i would go with the person!
But its MUCH easier when the person knows someone or even know where to go yes?
Its not easy getting to the right office here, and to speak to the right person takes forever