This is quite a handful. It’s generally recommended that each topic is focused on a single point/request and this is to ensure that each topics gets its fair share of discussion.
Anyway, regarding the payroll taxes. I’m not sure if I understand your request.
There’s the deduction section where you can make deductions credited to the liability/expense account of your choice and there’s the contribution section which is in effect a debit to an expense and a credit to a third-party liability account.
I think that this is enough to achieve any accounting treatment.
In your case, withheld payroll taxes–as I understand–is the amount deducted by the employer from the employee so you should define a Payslip Deduction Item following this guide.
As for this:
there’s currently two separate ideas for that:
And for this:
It’s not something that’s likely to implemented anytime soon. You can search the forum for similar topics.